diff --git a/onnxruntime/core/providers/webnn/builders/helper.h b/onnxruntime/core/providers/webnn/builders/helper.h
index 3cbe3ce5a631a..301d795912443 100644
--- a/onnxruntime/core/providers/webnn/builders/helper.h
+++ b/onnxruntime/core/providers/webnn/builders/helper.h
@@ -97,6 +97,7 @@ static const InlinedHashMap<std::string, std::string> op_map = {
     {"Erf", "erf"},
     {"Not", "logicalNot"},
     {"Floor", "floor"},
+    {"Flatten", "flattenTo2d"},
     {"Sin", "sin"},
     {"Sqrt", "sqrt"},
     {"Relu", "relu"},
diff --git a/onnxruntime/core/providers/webnn/builders/impl/flatten_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/flatten_op_builder.cc
new file mode 100644
index 0000000000000..6c59ca451f333
--- /dev/null
+++ b/onnxruntime/core/providers/webnn/builders/impl/flatten_op_builder.cc
@@ -0,0 +1,58 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Intel Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+#include "core/common/safeint.h"
+#include "core/providers/common.h"
+#include "core/providers/shared/utils/utils.h"
+#include "core/providers/webnn/builders/helper.h"
+#include "core/providers/webnn/builders/model_builder.h"
+#include "core/providers/webnn/builders/op_builder_factory.h"
+
+#include "base_op_builder.h"
+
+namespace onnxruntime {
+namespace webnn {
+
+class FlattenOpBuilder : public BaseOpBuilder {
+  // Add operator related.
+ private:
+  Status AddToModelBuilderImpl(ModelBuilder& model_builder, const Node& node,
+                               const logging::Logger& logger) const override ORT_MUST_USE_RESULT;
+};
+
+// Add operator related.
+
+Status FlattenOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
+                                               const Node& node,
+                                               const logging::Logger& logger) const {
+  const auto& input_defs = node.InputDefs();
+  std::vector<int64_t> input_shape;
+  ORT_RETURN_IF(input_defs.size() < 1, "Flatten has no input tensor");
+  if (!GetShape(*input_defs[0], input_shape, logger)) {
+    return ORT_MAKE_STATUS(ONNXRUNTIME, INVALID_ARGUMENT,
+                           "FlattenOpBuilder::AddToModelBuilderImpl, cannot get input shape");
+  }
+  int64_t rank = input_shape.size();
+  NodeAttrHelper helper(node);
+  int64_t axis = helper.Get("axis", 1);
+  ORT_ENFORCE(axis >= -rank && axis <= rank, "axis ", axis,
+              " is not in valid range [-", rank, ",", rank, "]");
+  if (axis < 0) {
+    axis += rank;
+  }
+  emscripten::val inputs = model_builder.GetOperand(input_defs[0]->Name());
+  emscripten::val output = model_builder.GetBuilder().call<emscripten::val>("flattenTo2d", inputs,
+                                                                            static_cast<int32_t>(axis));
+
+  model_builder.AddOperand(node.OutputDefs()[0]->Name(), std::move(output));
+  return Status::OK();
+}
+
+void CreateFlattenOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations) {
+  op_registrations.builders.push_back(std::make_unique<FlattenOpBuilder>());
+  op_registrations.op_builder_map.emplace(op_type, op_registrations.builders.back().get());
+}
+
+}  // namespace webnn
+}  // namespace onnxruntime
diff --git a/onnxruntime/core/providers/webnn/builders/op_builder_factory.cc b/onnxruntime/core/providers/webnn/builders/op_builder_factory.cc
index a43fe4a41b92d..82a45719ec1c3 100644
--- a/onnxruntime/core/providers/webnn/builders/op_builder_factory.cc
+++ b/onnxruntime/core/providers/webnn/builders/op_builder_factory.cc
@@ -68,6 +68,10 @@ static OpBuilderRegistrations CreateOpBuilderRegistrations() {
     CreateGatherOpBuilder("Gather", op_registrations);
   }
 
+  {  // Flatten
+    CreateFlattenOpBuilder("Flatten", op_registrations);
+  }
+
   {  // Gemm/MatMul
     CreateGemmOpBuilder("Gemm", op_registrations);
     CreateGemmOpBuilder("MatMul", op_registrations);
diff --git a/onnxruntime/core/providers/webnn/builders/op_builder_factory.h b/onnxruntime/core/providers/webnn/builders/op_builder_factory.h
index b8cf7322f2fe9..8f8299e5138a4 100644
--- a/onnxruntime/core/providers/webnn/builders/op_builder_factory.h
+++ b/onnxruntime/core/providers/webnn/builders/op_builder_factory.h
@@ -27,6 +27,7 @@ void CreateClipOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_
 void CreateConvOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);
 void CreateConcatOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);
 void CreateExpandOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);
+void CreateFlattenOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);
 void CreateGatherOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);
 void CreateGemmOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);
 void CreatePoolOpBuilder(const std::string& op_type, OpBuilderRegistrations& op_registrations);