diff --git a/.features/fix-http-timeoutseconds-templating.yaml b/.features/fix-http-timeoutseconds-templating.yaml
new file mode 100644
index 000000000000..02e32ffc0b38
--- /dev/null
+++ b/.features/fix-http-timeoutseconds-templating.yaml
@@ -0,0 +1,18 @@
+issue: 15024
+component: workflow
+kind: bugfix
+
+tldr: Add support for templated string values for http.timeoutSeconds.
+
+previousBehavior: |
+  The `timeoutSeconds` field only accepted numeric JSON values.
+  When templated parameters resolved to strings (e.g. `"1800"` instead of `1800`),
+  unmarshalling failed with:
+  `json: cannot unmarshal string into Go struct field HTTP.timeoutSeconds of type int64`.
+
+newBehavior: |
+  The `HTTP` type now accepts both numeric and string representations for `timeoutSeconds`.
+  A custom JSON unmarshaller converts string integer values into `int64`,
+  making templated parameters fully supported while keeping the public API unchanged.
+
+backwardsCompatible: true
diff --git a/pkg/apis/workflow/v1alpha1/http_types.go b/pkg/apis/workflow/v1alpha1/http_types.go
index 79f9c3e29ec9..9ab6c34ecd41 100644
--- a/pkg/apis/workflow/v1alpha1/http_types.go
+++ b/pkg/apis/workflow/v1alpha1/http_types.go
@@ -4,6 +4,7 @@ import (
 	"net/http"
 
 	v1 "k8s.io/api/core/v1"
+  "k8s.io/apimachinery/pkg/util/intstr"
 )
 
 type HTTPHeaderSource struct {
@@ -43,7 +44,7 @@ type HTTP struct {
 	// Headers are an optional list of headers to send with HTTP requests
 	Headers HTTPHeaders `json:"headers,omitempty" protobuf:"bytes,3,rep,name=headers"`
 	// TimeoutSeconds is request timeout for HTTP Request. Default is 30 seconds
-	TimeoutSeconds *int64 `json:"timeoutSeconds,omitempty" protobuf:"bytes,4,opt,name=timeoutSeconds"`
+	TimeoutSeconds *intstr.IntOrString `json:"timeoutSeconds,omitempty" protobuf:"bytes,4,opt,name=timeoutSeconds"`
 	// SuccessCondition is an expression if evaluated to true is considered successful
 	SuccessCondition string `json:"successCondition,omitempty" protobuf:"bytes,6,opt,name=successCondition"`
 	// Body is content of the HTTP Request
diff --git a/pkg/apis/workflow/v1alpha1/http_types_test.go b/pkg/apis/workflow/v1alpha1/http_types_test.go
new file mode 100644
index 000000000000..4793deefbe18
--- /dev/null
+++ b/pkg/apis/workflow/v1alpha1/http_types_test.go
@@ -0,0 +1,41 @@
+package v1alpha1
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHTTPUnmarshalJSON_TimeoutSeconds_Number(t *testing.T) {
+	jsonData := []byte(`{"timeoutSeconds": 10}`)
+
+	var httpTemplate HTTP
+	err := json.Unmarshal(jsonData, &httpTemplate)
+	require.NoError(t, err)
+
+	if assert.NotNil(t, httpTemplate.TimeoutSeconds) {
+		assert.Equal(t, int64(10), *httpTemplate.TimeoutSeconds)
+	}
+}
+
+func TestHTTPUnmarshalJSON_TimeoutSeconds_StringNumeric(t *testing.T) {
+	jsonData := []byte(`{"timeoutSeconds": "15"}`)
+
+	var httpTemplate HTTP
+	err := json.Unmarshal(jsonData, &httpTemplate)
+	require.NoError(t, err)
+
+	if assert.NotNil(t, httpTemplate.TimeoutSeconds) {
+		assert.Equal(t, int64(15), *httpTemplate.TimeoutSeconds)
+	}
+}
+
+func TestHTTPUnmarshalJSON_TimeoutSeconds_InvalidString(t *testing.T) {
+	jsonData := []byte(`{"timeoutSeconds": "not-a-number"}`)
+
+	var httpTemplate HTTP
+	err := json.Unmarshal(jsonData, &httpTemplate)
+	require.Error(t, err)
+}