diff --git a/clang/include/clang/CIR/CIRToCIRPasses.h b/clang/include/clang/CIR/CIRToCIRPasses.h
index ec6d75332bed9..061b4462ed846 100644
--- a/clang/include/clang/CIR/CIRToCIRPasses.h
+++ b/clang/include/clang/CIR/CIRToCIRPasses.h
@@ -32,7 +32,8 @@ namespace cir {
 mlir::LogicalResult
 runCIRToCIRPasses(mlir::ModuleOp theModule, mlir::MLIRContext &mlirCtx,
                   clang::ASTContext &astCtx, bool enableVerifier,
-                  bool enableIdiomRecognizer, bool enableCIRSimplify);
+                  bool enableIdiomRecognizer, bool enableCIRSimplify,
+                  bool enableCallingConvLowering);
 
 } // namespace cir
 
diff --git a/clang/include/clang/CIR/Dialect/Passes.h b/clang/include/clang/CIR/Dialect/Passes.h
index d441dfcbc6c14..31332e968309f 100644
--- a/clang/include/clang/CIR/Dialect/Passes.h
+++ b/clang/include/clang/CIR/Dialect/Passes.h
@@ -34,6 +34,9 @@ std::unique_ptr<Pass> createGotoSolverPass();
 std::unique_ptr<Pass> createIdiomRecognizerPass();
 std::unique_ptr<Pass> createIdiomRecognizerPass(clang::ASTContext *astCtx);
 
+/// Create a pass to lower ABI-independent function definitions/calls.
+std::unique_ptr<Pass> createCallConvLoweringPass();
+
 void populateCIRPreLoweringPasses(mlir::OpPassManager &pm);
 
 //===----------------------------------------------------------------------===//
diff --git a/clang/include/clang/CIR/Dialect/Passes.td b/clang/include/clang/CIR/Dialect/Passes.td
index 32cd182aacec7..7f08221c965ca 100644
--- a/clang/include/clang/CIR/Dialect/Passes.td
+++ b/clang/include/clang/CIR/Dialect/Passes.td
@@ -195,4 +195,15 @@ def IdiomRecognizer : Pass<"cir-idiom-recognizer", "mlir::ModuleOp"> {
   let dependentDialects = ["cir::CIRDialect"];
 }
 
+def CallConvLowering : Pass<"cir-call-conv-lowering"> {
+  let summary = "Handle calling conventions for CIR functions";
+  let description = [{
+    This pass lowers CIR function definitions and calls according to the
+    calling conventions for the target architecture. This pass is necessary
+    to properly lower CIR functions to LLVM IR.
+  }];
+  let constructor = "mlir::createCallConvLoweringPass()";
+  let dependentDialects = ["cir::CIRDialect"];
+}
+
 #endif // CLANG_CIR_DIALECT_PASSES_TD
diff --git a/clang/include/clang/Frontend/FrontendOptions.h b/clang/include/clang/Frontend/FrontendOptions.h
index f7f51bc37c98d..26028fd82087c 100644
--- a/clang/include/clang/Frontend/FrontendOptions.h
+++ b/clang/include/clang/Frontend/FrontendOptions.h
@@ -426,6 +426,9 @@ class FrontendOptions {
   LLVM_PREFERRED_TYPE(bool)
   unsigned ClangIREnableIdiomRecognizer : 1;
 
+  // Enable Clang IR call conv lowering pass.
+  unsigned ClangIRCallConvLowering : 1;
+
   CodeCompleteOptions CodeCompleteOpts;
 
   /// Specifies the output format of the AST.
diff --git a/clang/include/clang/Options/Options.td b/clang/include/clang/Options/Options.td
index 215d4e885709c..a787c3fbcddae 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -3355,6 +3355,14 @@ def clangir_enable_idiom_recognizer : Flag<["-"], "clangir-enable-idiom-recogniz
   HelpText<"ClangIR: Enable Idiom Recognizer pass">,
   MarshallingInfoFlag<FrontendOpts<"ClangIREnableIdiomRecognizer">>;
 
+// FIXME(cir): Remove this option once all pre-existing tests are compatible with
+// the calling convention lowering pass.
+defm clangir_call_conv_lowering : BoolFOption<"clangir-call-conv-lowering",
+  FrontendOpts<"ClangIRCallConvLowering">, DefaultFalse,
+  PosFlag<SetTrue, [], [ClangOption, CC1Option], "Transform CIR to abide to calling conventions during lowering">,
+  NegFlag<SetFalse, [], [ClangOption, CC1Option], "Ignore calling convention during lowering">,
+  BothFlags<[], [ClangOption, CC1Option], "">>;
+
 defm clangir : BoolFOption<"clangir",
   FrontendOpts<"UseClangIRPipeline">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option], "Use the ClangIR pipeline to compile">,
diff --git a/clang/lib/CIR/Dialect/Transforms/CMakeLists.txt b/clang/lib/CIR/Dialect/Transforms/CMakeLists.txt
index 411bbc386b9d1..205e59dbb9eb4 100644
--- a/clang/lib/CIR/Dialect/Transforms/CMakeLists.txt
+++ b/clang/lib/CIR/Dialect/Transforms/CMakeLists.txt
@@ -11,6 +11,7 @@ add_clang_library(MLIRCIRTransforms
   LoweringPrepare.cpp
   GotoSolver.cpp
   IdiomRecognizer.cpp
+  CallConvLowering.cpp
 
   DEPENDS
   MLIRCIRPassIncGen
diff --git a/clang/lib/CIR/Dialect/Transforms/CallConvLowering.cpp b/clang/lib/CIR/Dialect/Transforms/CallConvLowering.cpp
new file mode 100644
index 0000000000000..1c166d5bd0c09
--- /dev/null
+++ b/clang/lib/CIR/Dialect/Transforms/CallConvLowering.cpp
@@ -0,0 +1,58 @@
+//===- CallConvLowering.cpp - Rewrites functions according to call convs --===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/IR/BuiltinOps.h"
+#include "mlir/Pass/Pass.h"
+#include "clang/CIR/Dialect/IR/CIRDialect.h"
+
+#define GEN_PASS_DEF_CALLCONVLOWERING
+#include "clang/CIR/Dialect/Passes.h.inc"
+
+namespace cir {
+
+struct CallConvLowering {
+  CallConvLowering(mlir::ModuleOp module) : module(module) {}
+
+  void lower(FuncOp op) {
+    // TODO(cir): Implement calling convention lowering for function definitions
+    // and calls once the upstream LowerModule has the necessary APIs.
+  }
+
+private:
+  mlir::ModuleOp module;
+};
+
+//===----------------------------------------------------------------------===//
+// Pass
+//===----------------------------------------------------------------------===//
+
+struct CallConvLoweringPass
+    : ::impl::CallConvLoweringBase<CallConvLoweringPass> {
+  using CallConvLoweringBase::CallConvLoweringBase;
+
+  void runOnOperation() override;
+  llvm::StringRef getArgument() const override {
+    return "cir-call-conv-lowering";
+  };
+};
+
+void CallConvLoweringPass::runOnOperation() {
+  auto module = mlir::dyn_cast<mlir::ModuleOp>(getOperation());
+  CallConvLowering cc(module);
+  module.walk([&](FuncOp op) { cc.lower(op); });
+}
+
+} // namespace cir
+
+namespace mlir {
+
+std::unique_ptr<mlir::Pass> createCallConvLoweringPass() {
+  return std::make_unique<cir::CallConvLoweringPass>();
+}
+
+} // namespace mlir
diff --git a/clang/lib/CIR/FrontendAction/CIRGenAction.cpp b/clang/lib/CIR/FrontendAction/CIRGenAction.cpp
index ab273539b1ce2..5d4e70d6724e1 100644
--- a/clang/lib/CIR/FrontendAction/CIRGenAction.cpp
+++ b/clang/lib/CIR/FrontendAction/CIRGenAction.cpp
@@ -122,7 +122,8 @@ class CIRGenConsumer : public clang::ASTConsumer {
       // Setup and run CIR pipeline.
       if (runCIRToCIRPasses(
               MlirModule, MlirCtx, C, !FEOptions.ClangIRDisableCIRVerifier,
-              FEOptions.ClangIREnableIdiomRecognizer, CGO.OptimizationLevel > 0)
+              FEOptions.ClangIREnableIdiomRecognizer, CGO.OptimizationLevel > 0,
+              FEOptions.ClangIRCallConvLowering)
               .failed()) {
         CI.getDiagnostics().Report(diag::err_cir_to_cir_transform_failed);
         return;
diff --git a/clang/lib/CIR/Lowering/CIRPasses.cpp b/clang/lib/CIR/Lowering/CIRPasses.cpp
index 7b93356a34c38..1cc00610d3fdb 100644
--- a/clang/lib/CIR/Lowering/CIRPasses.cpp
+++ b/clang/lib/CIR/Lowering/CIRPasses.cpp
@@ -20,7 +20,8 @@ namespace cir {
 mlir::LogicalResult
 runCIRToCIRPasses(mlir::ModuleOp theModule, mlir::MLIRContext &mlirContext,
                   clang::ASTContext &astContext, bool enableVerifier,
-                  bool enableIdiomRecognizer, bool enableCIRSimplify) {
+                  bool enableIdiomRecognizer, bool enableCIRSimplify,
+                  bool enableCallConvLowering) {
 
   llvm::TimeTraceScope scope("CIR To CIR Passes");
 
@@ -37,6 +38,11 @@ runCIRToCIRPasses(mlir::ModuleOp theModule, mlir::MLIRContext &mlirContext,
   pm.addPass(mlir::createCXXABILoweringPass());
   pm.addPass(mlir::createLoweringPreparePass(&astContext));
 
+  // FIXME(cir): This pass should run by default, but it is lacking support for
+  // several code bits. Once it's more mature, we should fix this.
+  if (enableCallConvLowering)
+    pm.addPass(mlir::createCallConvLoweringPass());
+
   pm.enableVerifier(enableVerifier);
   (void)mlir::applyPassManagerCLOptions(pm);
   return pm.run(theModule);
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index db82695f87d6b..e3edee10767e7 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5112,6 +5112,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (Args.hasArg(options::OPT_fclangir))
     CmdArgs.push_back("-fclangir");
 
+  if (Args.hasArg(options::OPT_fclangir_call_conv_lowering))
+    CmdArgs.push_back("-fclangir-call-conv-lowering");
+
   if (IsOpenMPDevice) {
     // We have to pass the triple of the host if compiling for an OpenMP device.
     std::string NormalizedTriple =
diff --git a/clang/test/CIR/Transforms/call-conv-lowering-pass.cpp b/clang/test/CIR/Transforms/call-conv-lowering-pass.cpp
new file mode 100644
index 0000000000000..5581a45e83071
--- /dev/null
+++ b/clang/test/CIR/Transforms/call-conv-lowering-pass.cpp
@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fclangir -fclangir-call-conv-lowering -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s
+
+// CHECK: cir.func {{.*}}@_Z5emptyv()
+void empty() {}