diff --git a/params/json.libevm.go b/params/json.libevm.go
index c9acefe949738..5a517fba98086 100644
--- a/params/json.libevm.go
+++ b/params/json.libevm.go
@@ -124,3 +124,27 @@ func toJSONRawMessages(v any) (map[string]json.RawMessage, error) {
 	}
 	return msgs, nil
 }
+
+// UnmarshalChainConfig JSON decodes the given data into the config and the extra
+// pointer arguments. The root JSON keys except the "extra" key are decoded into
+// the config argument, and the object at the "extra" key, if present, is decoded
+// into the extra argument. Note the extra argument must be a non-nil pointer or
+// an error would be returned.
+func UnmarshalChainConfig(data []byte, config *ChainConfig, extra any) (err error) {
+	err = json.Unmarshal(data, config)
+	if err != nil {
+		return fmt.Errorf("json decoding root chain config: %w", err)
+	}
+
+	jsonExtra := struct {
+		Extra any `json:"extra"`
+	}{
+		Extra: extra,
+	}
+	err = json.Unmarshal(data, &jsonExtra)
+	if err != nil {
+		return fmt.Errorf("json decoding extra chain config: %w", err)
+	}
+
+	return nil
+}
diff --git a/params/json.libevm_test.go b/params/json.libevm_test.go
index 70014e0d8d13c..202b0ae57938f 100644
--- a/params/json.libevm_test.go
+++ b/params/json.libevm_test.go
@@ -21,6 +21,7 @@ import (
 	"math/big"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/ava-labs/libevm/libevm/pseudo"
@@ -144,3 +145,60 @@ func TestChainConfigJSONRoundTrip(t *testing.T) {
 		})
 	}
 }
+
+func Test_UnmarshalChainConfig(t *testing.T) {
+	t.Parallel()
+
+	type testExtra struct {
+		Field string `json:"field"`
+	}
+
+	testCases := map[string]struct {
+		jsonData       string // string for convenience
+		expectedConfig ChainConfig
+		expectedExtra  any
+		errMessage     string
+	}{
+		"invalid_json": {
+			expectedExtra: testExtra{},
+			errMessage:    "json decoding root chain config: unexpected end of JSON input",
+		},
+		"no_extra": {
+			jsonData:       `{"chainId": 1}`,
+			expectedConfig: ChainConfig{ChainID: big.NewInt(1)},
+			expectedExtra:  testExtra{},
+		},
+		"wrong_extra_type": {
+			jsonData:       `{"chainId": 1, "extra": 1}`,
+			expectedConfig: ChainConfig{ChainID: big.NewInt(1)},
+			expectedExtra:  testExtra{},
+			errMessage: "json decoding extra chain config: " +
+				"json: cannot unmarshal number into Go struct field " +
+				".extra of type params.testExtra",
+		},
+		"extra_success": {
+			jsonData:       `{"chainId": 1, "extra": {"field":"value"}}`,
+			expectedConfig: ChainConfig{ChainID: big.NewInt(1)},
+			expectedExtra:  testExtra{Field: "value"},
+		},
+	}
+
+	for name, testCase := range testCases {
+		testCase := testCase
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			data := []byte(testCase.jsonData)
+			config := ChainConfig{}
+			var extra testExtra
+			err := UnmarshalChainConfig(data, &config, &extra)
+			if testCase.errMessage == "" {
+				assert.NoError(t, err)
+			} else {
+				assert.EqualError(t, err, testCase.errMessage)
+			}
+			assert.Equal(t, testCase.expectedConfig, config)
+			assert.Equal(t, testCase.expectedExtra, extra)
+		})
+	}
+}