diff --git a/mlir/include/mlir/Transforms/DialectConversion.h b/mlir/include/mlir/Transforms/DialectConversion.h
--- a/mlir/include/mlir/Transforms/DialectConversion.h
+++ b/mlir/include/mlir/Transforms/DialectConversion.h
@@ -863,6 +863,14 @@
 LogicalResult applyAnalysisConversion(Operation *op, ConversionTarget &target,
                                       const FrozenRewritePatternList &patterns,
                                       DenseSet<Operation *> &convertedOps);
+
+/// Report whether the given operation, and all nested operations, are legal as
+/// specified by the give ConversionTarget. Returns failure and emits error
+/// diagnostics if any operations are not legal as well as a summary of the
+/// illegal operations.
+LogicalResult verifyAllOperationsAreLegal(Operation *op,
+                                          ConversionTarget &target);
+
 } // end namespace mlir
 
 #endif // MLIR_TRANSFORMS_DIALECTCONVERSION_H_
diff --git a/mlir/lib/Transforms/Utils/DialectConversion.cpp b/mlir/lib/Transforms/Utils/DialectConversion.cpp
--- a/mlir/lib/Transforms/Utils/DialectConversion.cpp
+++ b/mlir/lib/Transforms/Utils/DialectConversion.cpp
@@ -13,9 +13,11 @@
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/FunctionSupport.h"
 #include "mlir/Rewrite/PatternApplicator.h"
+#include "mlir/Support/LLVM.h"
 #include "mlir/Transforms/Utils.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/SaveAndRestore.h"
@@ -2784,3 +2786,37 @@
   return applyAnalysisConversion(llvm::makeArrayRef(op), target, patterns,
                                  convertedOps);
 }
+
+static void emitLegalizationErrors(Location loc,
+                                   const DenseSet<Operation *> &illegalOps) {
+  // Print op errors for each of the illegal ops that still remain.
+  llvm::MapVector<StringRef, int> opNameCounts;
+  for (Operation *illegalOp : illegalOps) {
+    StringRef opName = illegalOp->getName().getStringRef();
+    opNameCounts[opName]++;
+    illegalOp->emitOpError() << ": illegal op still exists";
+  }
+
+  std::vector<std::string> errorMessages;
+  errorMessages.reserve(opNameCounts.size());
+  for (const auto &opInfo : opNameCounts) {
+    errorMessages.push_back(
+        llvm::formatv("\t{0} (count: {1})", opInfo.first, opInfo.second));
+  }
+  emitError(loc) << "The following illegal operations still remain: \n"
+                 << llvm::join(errorMessages, "\n") << "\n";
+}
+
+LogicalResult mlir::verifyAllOperationsAreLegal(Operation *op,
+                                                ConversionTarget &target) {
+  DenseSet<Operation *> illegalOps;
+  op->walk([&](Operation *op) {
+    if (!target.isLegal(op)) {
+      illegalOps.insert(op);
+    }
+  });
+  if (illegalOps.empty())
+    return success();
+  emitLegalizationErrors(op->getLoc(), illegalOps);
+  return failure();
+}
diff --git a/mlir/test/Transforms/test-verify-fully-converted.mlir b/mlir/test/Transforms/test-verify-fully-converted.mlir
new file mode 100644
--- /dev/null
+++ b/mlir/test/Transforms/test-verify-fully-converted.mlir
@@ -0,0 +1,16 @@
+// RUN: mlir-opt %s -split-input-file -test-verify-fully-converted -verify-diagnostics -allow-unregistered-dialect
+
+// -----
+
+// expected-error@+1 {{The following illegal operations still remain}}
+module {
+  func @f() -> () {
+    // expected-error@+1 {{'test.some_op' op : illegal op still exists}}
+    %0 = "test.some_op"() : () -> tensor<i32>
+    // expected-error@+1 {{'test.other_op' op : illegal op still exists}}
+    %1 = "test.other_op"() : () -> tensor<i32>
+    return
+  }
+}
+
+
diff --git a/mlir/test/lib/Transforms/CMakeLists.txt b/mlir/test/lib/Transforms/CMakeLists.txt
--- a/mlir/test/lib/Transforms/CMakeLists.txt
+++ b/mlir/test/lib/Transforms/CMakeLists.txt
@@ -32,6 +32,7 @@
   TestSCFUtils.cpp
   TestSparsification.cpp
   TestVectorTransforms.cpp
+  TestVerifyFullyConverted.cpp
 
   EXCLUDE_FROM_LIBMLIR
 
diff --git a/mlir/test/lib/Transforms/TestVerifyFullyConverted.cpp b/mlir/test/lib/Transforms/TestVerifyFullyConverted.cpp
new file mode 100644
--- /dev/null
+++ b/mlir/test/lib/Transforms/TestVerifyFullyConverted.cpp
@@ -0,0 +1,38 @@
+//===- TestVerifyFullyConverted.cpp - Test VectorTransfers lowering ---===//
+//
+// 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 "TestDialect.h"
+#include "mlir/Pass/Pass.h"
+#include "mlir/Transforms/DialectConversion.h"
+
+using namespace mlir;
+
+namespace {
+class TestVerifyFullyConvertedPass
+    : public PassWrapper<TestVerifyFullyConvertedPass, OperationPass<>> {
+public:
+  void runOnOperation() override {
+    ConversionTarget target(getContext());
+    target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
+    target.addIllegalDialect<test::TestDialect>();
+    if (failed(verifyAllOperationsAreLegal(getOperation(), target))) {
+      return signalPassFailure();
+    }
+  }
+};
+} // namespace
+
+namespace mlir {
+namespace test {
+void registerVerifyFullyConverted() {
+  PassRegistration<TestVerifyFullyConvertedPass>(
+      "test-verify-fully-converted",
+      "Test verification that no illegal ops remain");
+}
+} // namespace test
+} // namespace mlir
diff --git a/mlir/tools/mlir-opt/mlir-opt.cpp b/mlir/tools/mlir-opt/mlir-opt.cpp
--- a/mlir/tools/mlir-opt/mlir-opt.cpp
+++ b/mlir/tools/mlir-opt/mlir-opt.cpp
@@ -56,6 +56,7 @@
 namespace test {
 void registerConvertCallOpPass();
 void registerInliner();
+void registerVerifyFullyConverted();
 void registerMemRefBoundCheck();
 void registerPatternsTestPass();
 void registerSimpleParametricTilingPass();
@@ -125,6 +126,7 @@
 
   test::registerConvertCallOpPass();
   test::registerInliner();
+  test::registerVerifyFullyConverted();
   test::registerMemRefBoundCheck();
   test::registerPatternsTestPass();
   test::registerSimpleParametricTilingPass();