diff --git a/cpp/src/arrow/compute/row/encode_internal.cc b/cpp/src/arrow/compute/row/encode_internal.cc
index 0e2720a2866..0d57cb83bfd 100644
--- a/cpp/src/arrow/compute/row/encode_internal.cc
+++ b/cpp/src/arrow/compute/row/encode_internal.cc
@@ -279,7 +279,7 @@ void EncoderInteger::Decode(uint32_t start_row, uint32_t num_rows,
       case 4:
         for (uint32_t i = 0; i < num_rows; ++i) {
           reinterpret_cast<uint32_t*>(col_base)[i] = *reinterpret_cast<const uint32_t*>(
-              rows.fixed_length_rows(start_row + i + offset_within_row));
+              rows.fixed_length_rows(start_row + i) + offset_within_row);
         }
         break;
       case 8:
diff --git a/cpp/src/arrow/compute/row/grouper_test.cc b/cpp/src/arrow/compute/row/grouper_test.cc
index 0b8d8da0a6b..3ed2fde2e94 100644
--- a/cpp/src/arrow/compute/row/grouper_test.cc
+++ b/cpp/src/arrow/compute/row/grouper_test.cc
@@ -825,6 +825,28 @@ TEST(Grouper, DictKey) {
                                   g.grouper_->Consume(dict_span));
 }
 
+// GH-45393: Test combinations of numeric type keys of different lengths.
+TEST(Grouper, MultipleIntKeys) {
+  auto types = NumericTypes();
+  for (auto& t0 : types) {
+    ARROW_SCOPED_TRACE("t0=", t0->ToString());
+    for (auto& t1 : types) {
+      ARROW_SCOPED_TRACE("t1=", t1->ToString());
+      for (auto& t2 : types) {
+        ARROW_SCOPED_TRACE("t2=", t2->ToString());
+        TestGrouper g({t0, t1, t2});
+
+        g.ExpectConsume(R"([[0, 1, 2], [0, 1, 2]])", "[0, 0]");
+        g.ExpectConsume(R"([[0, 1, 2], [null, 1, 2]])", "[0, 1]");
+        g.ExpectConsume(R"([[0, 1, 2], [0, null, 2]])", "[0, 2]");
+        g.ExpectConsume(R"([[0, 1, 2], [0, 1, null]])", "[0, 3]");
+
+        g.ExpectUniques("[[0, 1, 2], [null, 1, 2], [0, null, 2], [0, 1, null]]");
+      }
+    }
+  }
+}
+
 TEST(Grouper, StringInt64Key) {
   TestGrouper g({utf8(), int64()});