diff --git a/.changeset/tall-falcons-yawn.md b/.changeset/tall-falcons-yawn.md
new file mode 100644
index 00000000000..98b90e5994b
--- /dev/null
+++ b/.changeset/tall-falcons-yawn.md
@@ -0,0 +1,5 @@
+---
+"chainlink": patch
+---
+
+#added the ability to define a fallback.toml override config using CL_CHAIN_DEFAULTS env var
diff --git a/core/chains/evm/config/toml/defaults.go b/core/chains/evm/config/toml/defaults.go
index 6f03575056b..60da9bded1b 100644
--- a/core/chains/evm/config/toml/defaults.go
+++ b/core/chains/evm/config/toml/defaults.go
@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"embed"
 	"fmt"
-	"io"
+	"io/fs"
 	"log"
 	"os"
 	"path/filepath"
@@ -19,7 +19,6 @@ import (
 )
 
 var (
-
 	//go:embed defaults/*.toml
 	defaultsFS   embed.FS
 	fallback     Chain
@@ -33,48 +32,24 @@ var (
 )
 
 func init() {
-	// read the defaults first
+	var (
+		fb  *Chain
+		err error
+	)
 
-	fes, err := defaultsFS.ReadDir("defaults")
+	// read all default configs
+	DefaultIDs, defaultNames, defaults, fb, err = initDefaults(defaultsFS.ReadDir, defaultsFS.ReadFile, "defaults")
 	if err != nil {
-		log.Fatalf("failed to read defaults/: %v", err)
+		log.Fatalf("failed to read defaults: %s", err)
 	}
-	for _, fe := range fes {
-		path := filepath.Join("defaults", fe.Name())
-		b, err2 := defaultsFS.ReadFile(path)
-		if err2 != nil {
-			log.Fatalf("failed to read %q: %v", path, err2)
-		}
-		var config = struct {
-			ChainID *big.Big
-			Chain
-		}{}
 
-		if err3 := cconfig.DecodeTOML(bytes.NewReader(b), &config); err3 != nil {
-			log.Fatalf("failed to decode %q: %v", path, err3)
-		}
-		if fe.Name() == "fallback.toml" {
-			if config.ChainID != nil {
-				log.Fatalf("fallback ChainID must be nil, not: %s", config.ChainID)
-			}
-			fallback = config.Chain
-			continue
-		}
-		if config.ChainID == nil {
-			log.Fatalf("missing ChainID: %s", path)
-		}
-		DefaultIDs = append(DefaultIDs, config.ChainID)
-		id := config.ChainID.String()
-		if _, ok := defaults[id]; ok {
-			log.Fatalf("%q contains duplicate ChainID: %s", path, id)
-		}
-		defaults[id] = config.Chain
-		defaultNames[id] = strings.ReplaceAll(strings.TrimSuffix(fe.Name(), ".toml"), "_", " ")
+	if fb == nil {
+		log.Fatal("failed to set fallback chain config")
 	}
-	slices.SortFunc(DefaultIDs, func(a, b *big.Big) int {
-		return a.Cmp(b)
-	})
 
+	fallback = *fb
+
+	// check for and apply any overrides
 	// read the custom defaults overrides
 	dir := env.CustomDefaults.Get()
 	if dir == "" {
@@ -83,54 +58,99 @@ func init() {
 	}
 
 	// use evm overrides specifically
-	evmDir := fmt.Sprintf("%s/evm", dir)
+	_, _, customDefaults, fb, err = initDefaults(os.ReadDir, os.ReadFile, dir+"/evm")
+	if err != nil {
+		log.Fatalf("failed to read custom overrides: %s", err)
+	}
 
-	// Read directory contents for evm only
-	entries, err := os.ReadDir(evmDir)
+	if fb != nil {
+		fallback = *fb
+	}
+}
+
+func initDefaults(
+	dirReader func(name string) ([]fs.DirEntry, error),
+	fileReader func(name string) ([]byte, error),
+	root string,
+) ([]*big.Big, map[string]string, map[string]Chain, *Chain, error) {
+	entries, err := dirReader(root)
 	if err != nil {
-		log.Fatalf("error reading evm custom defaults override directory: %v", err)
-		return
+		return nil, nil, nil, nil, fmt.Errorf("failed to read directory: %w", err)
 	}
 
+	var fb *Chain
+
+	ids := make([]*big.Big, 0)
+	configs := make(map[string]Chain)
+	names := make(map[string]string)
+
 	for _, entry := range entries {
 		if entry.IsDir() {
 			// Skip directories
 			continue
 		}
 
-		path := evmDir + "/" + entry.Name()
-		file, err := os.Open(path)
-		if err != nil {
-			log.Fatalf("error opening file (name: %v) in custom defaults override directory: %v", entry.Name(), err)
-		}
+		// read the file to bytes
+		path := filepath.Join(root, entry.Name())
 
-		// Read file contents
-		b, err := io.ReadAll(file)
-		file.Close()
+		chainID, chain, err := readConfig(path, fileReader)
 		if err != nil {
-			log.Fatalf("error reading file (name: %v) contents in custom defaults override directory: %v", entry.Name(), err)
+			return nil, nil, nil, nil, err
 		}
 
-		var config = struct {
-			ChainID *big.Big
-			Chain
-		}{}
+		if entry.Name() == "fallback.toml" {
+			if chainID != nil {
+				return nil, nil, nil, nil, fmt.Errorf("fallback ChainID must be nil: found: %s", chainID)
+			}
+
+			fb = &chain
 
-		if err := cconfig.DecodeTOML(bytes.NewReader(b), &config); err != nil {
-			log.Fatalf("failed to decode %q in custom defaults override directory: %v", path, err)
+			continue
 		}
 
-		if config.ChainID == nil {
-			log.Fatalf("missing ChainID in: %s in custom defaults override directory. exiting", path)
+		// ensure ChainID is set
+		if chainID == nil {
+			return nil, nil, nil, nil, fmt.Errorf("missing ChainID: %s", path)
 		}
 
-		id := config.ChainID.String()
+		ids = append(ids, chainID)
 
-		if _, ok := customDefaults[id]; ok {
+		// ChainID as a default should not be duplicated
+		id := chainID.String()
+		if _, ok := configs[id]; ok {
 			log.Fatalf("%q contains duplicate ChainID: %s", path, id)
 		}
-		customDefaults[id] = config.Chain
+
+		// set lookups
+		configs[id] = chain
+		names[id] = strings.ReplaceAll(strings.TrimSuffix(entry.Name(), ".toml"), "_", " ")
 	}
+
+	// sort IDs in numeric order
+	slices.SortFunc(ids, func(a, b *big.Big) int {
+		return a.Cmp(b)
+	})
+
+	return ids, names, configs, fb, nil
+}
+
+func readConfig(path string, reader func(name string) ([]byte, error)) (*big.Big, Chain, error) {
+	bts, err := reader(path)
+	if err != nil {
+		return nil, Chain{}, fmt.Errorf("error reading file: %w", err)
+	}
+
+	var config = struct {
+		ChainID *big.Big
+		Chain
+	}{}
+
+	// decode from toml to a chain config
+	if err := cconfig.DecodeTOML(bytes.NewReader(bts), &config); err != nil {
+		return nil, Chain{}, fmt.Errorf("error in TOML decoding %s: %w", path, err)
+	}
+
+	return config.ChainID, config.Chain, nil
 }
 
 // DefaultsNamed returns the default Chain values, optionally for the given chainID, as well as a name if the chainID is known.
diff --git a/testdata/scripts/node/validate/fallback-override.txtar b/testdata/scripts/node/validate/fallback-override.txtar
new file mode 100644
index 00000000000..91feb48693d
--- /dev/null
+++ b/testdata/scripts/node/validate/fallback-override.txtar
@@ -0,0 +1,552 @@
+# test with defaults
+env CL_CHAIN_DEFAULTS=
+exec chainlink node -c config.toml -s secrets.toml validate
+cmp stdout out.txt
+
+# test with fallback override
+env CL_CHAIN_DEFAULTS=default_overrides
+exec chainlink node -c config.toml -s secrets.toml validate
+! cmp stdout out.txt
+
+-- default_overrides/evm/fallback.toml --
+AutoCreateKey = true
+BlockBackfillDepth = 1000000
+BlockBackfillSkip = false
+FinalityDepth = 50
+FinalityTagEnabled = false
+LogBackfillBatchSize = 1000
+LogPollInterval = '15s'
+LogKeepBlocksDepth = 100000
+LogPrunePageSize = 0
+BackupLogPollerBlockDelay = 100
+MinContractPayment = '.00001 link'
+MinIncomingConfirmations = 3
+NonceAutoSync = true
+NoNewHeadsThreshold = '3m'
+RPCDefaultBatchSize = 250
+RPCBlockQueryDelay = 1
+FinalizedBlockOffset = 0
+NoNewFinalizedHeadsThreshold = '0'
+LogBroadcasterEnabled = true
+
+[Transactions]
+ForwardersEnabled = false
+MaxInFlight = 16
+MaxQueued = 250
+ReaperInterval = '1h'
+ReaperThreshold = '168h'
+ResendAfterThreshold = '1m'
+
+[Transactions.AutoPurge]
+Enabled = false
+
+[BalanceMonitor]
+Enabled = true
+
+[GasEstimator]
+Mode = 'BlockHistory'
+PriceDefault = '20 gwei'
+PriceMax = '115792089237316195423570985008687907853269984665.640564039457584007913129639935 tether'
+PriceMin = '1 gwei'
+LimitDefault = 500_000
+LimitMax = 500_000
+LimitMultiplier = '1'
+LimitTransfer = 21_000
+BumpMin = '5 gwei'
+BumpPercent = 20
+BumpThreshold = 3
+EIP1559DynamicFees = false
+FeeCapDefault = '100 gwei'
+TipCapDefault = '1'
+TipCapMin = '1'
+EstimateLimit = false
+
+[GasEstimator.BlockHistory]
+BatchSize = 25
+BlockHistorySize = 8
+CheckInclusionBlocks = 12
+CheckInclusionPercentile = 90
+TransactionPercentile = 60
+
+[GasEstimator.FeeHistory]
+CacheTimeout = '10s'
+
+[HeadTracker]
+HistoryDepth = 100
+MaxBufferSize = 3
+SamplingInterval = '1s'
+FinalityTagBypass = true
+MaxAllowedFinalityDepth = 10000
+PersistenceEnabled = true
+
+[NodePool]
+PollFailureThreshold = 5
+PollInterval = '10s'
+SelectionMode = 'HighestHead'
+SyncThreshold = 5
+LeaseDuration = '0s'
+NodeIsSyncingEnabled = false
+FinalizedBlockPollInterval = '5s'
+EnforceRepeatableRead = true
+DeathDeclarationDelay = '1m'
+NewHeadsPollInterval = '0s'
+
+[OCR]
+ContractConfirmations = 4
+ContractTransmitterTransmitTimeout = '10s'
+DatabaseTimeout = '10s'
+DeltaCOverride = '168h'
+DeltaCJitterOverride = '1h'
+ObservationGracePeriod = '1s'
+
+[OCR2.Automation]
+GasLimit = 5400000
+
+[Workflow]
+GasLimitDefault = 400_000
+
+-- config.toml --
+Log.Level = 'debug'
+
+[[EVM]]
+ChainID = '1'
+
+[[EVM.Nodes]]
+Name = 'fake'
+WSURL = 'wss://foo.bar/ws'
+HTTPURL = 'https://foo.bar'
+
+-- secrets.toml --
+[Database]
+URL = 'postgresql://user:pass1234567890abcd@localhost:5432/dbname?sslmode=disable'
+
+[Password]
+Keystore = 'keystore_pass'
+
+-- out.txt --
+# Secrets:
+[Database]
+URL = 'xxxxx'
+AllowSimplePasswords = false
+
+[Password]
+Keystore = 'xxxxx'
+
+# Input Configuration:
+[Log]
+Level = 'debug'
+
+[[EVM]]
+ChainID = '1'
+
+[[EVM.Nodes]]
+Name = 'fake'
+WSURL = 'wss://foo.bar/ws'
+HTTPURL = 'https://foo.bar'
+
+# Effective Configuration, with defaults applied:
+InsecureFastScrypt = false
+RootDir = '~/.chainlink'
+ShutdownGracePeriod = '5s'
+
+[Feature]
+FeedsManager = true
+LogPoller = false
+UICSAKeys = false
+CCIP = true
+MultiFeedsManagers = false
+
+[Database]
+DefaultIdleInTxSessionTimeout = '1h0m0s'
+DefaultLockTimeout = '15s'
+DefaultQueryTimeout = '10s'
+LogQueries = false
+MaxIdleConns = 10
+MaxOpenConns = 100
+MigrateOnStartup = true
+
+[Database.Backup]
+Dir = ''
+Frequency = '1h0m0s'
+Mode = 'none'
+OnVersionUpgrade = true
+
+[Database.Listener]
+MaxReconnectDuration = '10m0s'
+MinReconnectInterval = '1m0s'
+FallbackPollInterval = '30s'
+
+[Database.Lock]
+Enabled = true
+LeaseDuration = '10s'
+LeaseRefreshInterval = '1s'
+
+[TelemetryIngress]
+UniConn = false
+Logging = false
+BufferSize = 100
+MaxBatchSize = 50
+SendInterval = '500ms'
+SendTimeout = '10s'
+UseBatchSend = true
+
+[AuditLogger]
+Enabled = false
+ForwardToUrl = ''
+JsonWrapperKey = ''
+Headers = []
+
+[Log]
+Level = 'debug'
+JSONConsole = false
+UnixTS = false
+
+[Log.File]
+Dir = ''
+MaxSize = '5.12gb'
+MaxAgeDays = 0
+MaxBackups = 1
+
+[WebServer]
+AuthenticationMethod = 'local'
+AllowOrigins = 'http://localhost:3000,http://localhost:6688'
+BridgeResponseURL = ''
+BridgeCacheTTL = '0s'
+HTTPWriteTimeout = '10s'
+HTTPPort = 6688
+SecureCookies = true
+SessionTimeout = '15m0s'
+SessionReaperExpiration = '240h0m0s'
+HTTPMaxSize = '32.77kb'
+StartTimeout = '15s'
+ListenIP = '0.0.0.0'
+
+[WebServer.LDAP]
+ServerTLS = true
+SessionTimeout = '15m0s'
+QueryTimeout = '2m0s'
+BaseUserAttr = 'uid'
+BaseDN = ''
+UsersDN = 'ou=users'
+GroupsDN = 'ou=groups'
+ActiveAttribute = ''
+ActiveAttributeAllowedValue = ''
+AdminUserGroupCN = 'NodeAdmins'
+EditUserGroupCN = 'NodeEditors'
+RunUserGroupCN = 'NodeRunners'
+ReadUserGroupCN = 'NodeReadOnly'
+UserApiTokenEnabled = false
+UserAPITokenDuration = '240h0m0s'
+UpstreamSyncInterval = '0s'
+UpstreamSyncRateLimit = '2m0s'
+
+[WebServer.MFA]
+RPID = ''
+RPOrigin = ''
+
+[WebServer.RateLimit]
+Authenticated = 1000
+AuthenticatedPeriod = '1m0s'
+Unauthenticated = 5
+UnauthenticatedPeriod = '20s'
+
+[WebServer.TLS]
+CertPath = ''
+ForceRedirect = false
+Host = ''
+HTTPSPort = 6689
+KeyPath = ''
+ListenIP = '0.0.0.0'
+
+[JobPipeline]
+ExternalInitiatorsEnabled = false
+MaxRunDuration = '10m0s'
+MaxSuccessfulRuns = 10000
+ReaperInterval = '1h0m0s'
+ReaperThreshold = '24h0m0s'
+ResultWriteQueueDepth = 100
+VerboseLogging = true
+
+[JobPipeline.HTTPRequest]
+DefaultTimeout = '15s'
+MaxSize = '32.77kb'
+
+[FluxMonitor]
+DefaultTransactionQueueDepth = 1
+SimulateTransactions = false
+
+[OCR2]
+Enabled = false
+ContractConfirmations = 3
+BlockchainTimeout = '20s'
+ContractPollInterval = '1m0s'
+ContractSubscribeInterval = '2m0s'
+ContractTransmitterTransmitTimeout = '10s'
+DatabaseTimeout = '10s'
+KeyBundleID = '0000000000000000000000000000000000000000000000000000000000000000'
+CaptureEATelemetry = false
+CaptureAutomationCustomTelemetry = true
+DefaultTransactionQueueDepth = 1
+SimulateTransactions = false
+TraceLogging = false
+
+[OCR]
+Enabled = false
+ObservationTimeout = '5s'
+BlockchainTimeout = '20s'
+ContractPollInterval = '1m0s'
+ContractSubscribeInterval = '2m0s'
+DefaultTransactionQueueDepth = 1
+KeyBundleID = '0000000000000000000000000000000000000000000000000000000000000000'
+SimulateTransactions = false
+TransmitterAddress = ''
+CaptureEATelemetry = false
+TraceLogging = false
+
+[P2P]
+IncomingMessageBufferSize = 10
+OutgoingMessageBufferSize = 10
+PeerID = ''
+TraceLogging = false
+
+[P2P.V2]
+Enabled = true
+AnnounceAddresses = []
+DefaultBootstrappers = []
+DeltaDial = '15s'
+DeltaReconcile = '1m0s'
+ListenAddresses = []
+
+[Keeper]
+DefaultTransactionQueueDepth = 1
+GasPriceBufferPercent = 20
+GasTipCapBufferPercent = 20
+BaseFeeBufferPercent = 20
+MaxGracePeriod = 100
+TurnLookBack = 1000
+
+[Keeper.Registry]
+CheckGasOverhead = 200000
+PerformGasOverhead = 300000
+MaxPerformDataSize = 5000
+SyncInterval = '30m0s'
+SyncUpkeepQueueSize = 10
+
+[AutoPprof]
+Enabled = false
+ProfileRoot = ''
+PollInterval = '10s'
+GatherDuration = '10s'
+GatherTraceDuration = '5s'
+MaxProfileSize = '100.00mb'
+CPUProfileRate = 1
+MemProfileRate = 1
+BlockProfileRate = 1
+MutexProfileFraction = 1
+MemThreshold = '4.00gb'
+GoroutineThreshold = 5000
+
+[Pyroscope]
+ServerAddress = ''
+Environment = 'mainnet'
+
+[Sentry]
+Debug = false
+DSN = ''
+Environment = ''
+Release = ''
+
+[Insecure]
+DevWebServer = false
+OCRDevelopmentMode = false
+InfiniteDepthQueries = false
+DisableRateLimiting = false
+
+[Tracing]
+Enabled = false
+CollectorTarget = ''
+NodeID = ''
+SamplingRatio = 0.0
+Mode = 'tls'
+TLSCertPath = ''
+
+[Mercury]
+VerboseLogging = false
+
+[Mercury.Cache]
+LatestReportTTL = '1s'
+MaxStaleAge = '1h0m0s'
+LatestReportDeadline = '5s'
+
+[Mercury.TLS]
+CertFile = ''
+
+[Mercury.Transmitter]
+TransmitQueueMaxSize = 10000
+TransmitTimeout = '5s'
+TransmitConcurrency = 100
+
+[Capabilities]
+[Capabilities.Peering]
+IncomingMessageBufferSize = 10
+OutgoingMessageBufferSize = 10
+PeerID = ''
+TraceLogging = false
+
+[Capabilities.Peering.V2]
+Enabled = false
+AnnounceAddresses = []
+DefaultBootstrappers = []
+DeltaDial = '15s'
+DeltaReconcile = '1m0s'
+ListenAddresses = []
+
+[Capabilities.Dispatcher]
+SupportedVersion = 1
+ReceiverBufferSize = 10000
+
+[Capabilities.Dispatcher.RateLimit]
+GlobalRPS = 800.0
+GlobalBurst = 1000
+PerSenderRPS = 10.0
+PerSenderBurst = 50
+
+[Capabilities.ExternalRegistry]
+Address = ''
+NetworkID = 'evm'
+ChainID = '1'
+
+[Capabilities.WorkflowRegistry]
+Address = ''
+NetworkID = 'evm'
+ChainID = '1'
+
+[Capabilities.GatewayConnector]
+ChainIDForNodeKey = ''
+NodeAddress = ''
+DonID = ''
+WSHandshakeTimeoutMillis = 0
+AuthMinChallengeLen = 0
+AuthTimestampToleranceSec = 0
+
+[[Capabilities.GatewayConnector.Gateways]]
+ID = ''
+URL = ''
+
+[Telemetry]
+Enabled = false
+CACertFile = ''
+Endpoint = ''
+InsecureConnection = false
+TraceSampleRatio = 0.01
+EmitterBatchProcessor = true
+EmitterExportTimeout = '1s'
+
+[[EVM]]
+ChainID = '1'
+AutoCreateKey = true
+BlockBackfillDepth = 10
+BlockBackfillSkip = false
+FinalityDepth = 50
+FinalityTagEnabled = true
+LinkContractAddress = '0x514910771AF9Ca656af840dff83E8264EcF986CA'
+LogBackfillBatchSize = 1000
+LogPollInterval = '15s'
+LogKeepBlocksDepth = 100000
+LogPrunePageSize = 0
+BackupLogPollerBlockDelay = 100
+MinIncomingConfirmations = 3
+MinContractPayment = '0.1 link'
+NonceAutoSync = true
+NoNewHeadsThreshold = '3m0s'
+OperatorFactoryAddress = '0x3E64Cd889482443324F91bFA9c84fE72A511f48A'
+LogBroadcasterEnabled = true
+RPCDefaultBatchSize = 250
+RPCBlockQueryDelay = 1
+FinalizedBlockOffset = 0
+NoNewFinalizedHeadsThreshold = '9m0s'
+
+[EVM.Transactions]
+Enabled = true
+ForwardersEnabled = false
+MaxInFlight = 16
+MaxQueued = 250
+ReaperInterval = '1h0m0s'
+ReaperThreshold = '168h0m0s'
+ResendAfterThreshold = '1m0s'
+
+[EVM.Transactions.AutoPurge]
+Enabled = false
+
+[EVM.BalanceMonitor]
+Enabled = true
+
+[EVM.GasEstimator]
+Mode = 'BlockHistory'
+PriceDefault = '20 gwei'
+PriceMax = '115792089237316195423570985008687907853269984665.640564039457584007913129639935 tether'
+PriceMin = '1 gwei'
+LimitDefault = 500000
+LimitMax = 500000
+LimitMultiplier = '1'
+LimitTransfer = 21000
+EstimateLimit = false
+BumpMin = '5 gwei'
+BumpPercent = 20
+BumpThreshold = 3
+EIP1559DynamicFees = true
+FeeCapDefault = '100 gwei'
+TipCapDefault = '1 wei'
+TipCapMin = '1 wei'
+
+[EVM.GasEstimator.BlockHistory]
+BatchSize = 25
+BlockHistorySize = 4
+CheckInclusionBlocks = 12
+CheckInclusionPercentile = 90
+TransactionPercentile = 50
+
+[EVM.GasEstimator.FeeHistory]
+CacheTimeout = '10s'
+
+[EVM.HeadTracker]
+HistoryDepth = 100
+MaxBufferSize = 3
+SamplingInterval = '1s'
+MaxAllowedFinalityDepth = 10000
+FinalityTagBypass = true
+PersistenceEnabled = true
+
+[EVM.NodePool]
+PollFailureThreshold = 5
+PollInterval = '10s'
+SelectionMode = 'HighestHead'
+SyncThreshold = 5
+LeaseDuration = '0s'
+NodeIsSyncingEnabled = false
+FinalizedBlockPollInterval = '5s'
+EnforceRepeatableRead = true
+DeathDeclarationDelay = '1m0s'
+NewHeadsPollInterval = '0s'
+
+[EVM.OCR]
+ContractConfirmations = 4
+ContractTransmitterTransmitTimeout = '10s'
+DatabaseTimeout = '10s'
+DeltaCOverride = '168h0m0s'
+DeltaCJitterOverride = '1h0m0s'
+ObservationGracePeriod = '1s'
+
+[EVM.OCR2]
+[EVM.OCR2.Automation]
+GasLimit = 10500000
+
+[EVM.Workflow]
+GasLimitDefault = 400000
+
+[[EVM.Nodes]]
+Name = 'fake'
+WSURL = 'wss://foo.bar/ws'
+HTTPURL = 'https://foo.bar'
+
+Valid configuration.