diff --git a/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc b/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc
index 8e7b626837f..adda9f376be 100644
--- a/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc
+++ b/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc
@@ -452,8 +452,9 @@ Status StringDataTransform(KernelContext* ctx, const ExecSpan& batch,
 
   const auto offsets = input.GetValues<offset_type>(1);
   int64_t offset_nbytes = (input.length + 1) * sizeof(offset_type);
-  if (input.offset == 0) {
-    // We can reuse offsets from input if the input owns it
+  if (input.offset == 0 && (input.length == 0 || offsets[0] == 0)) {
+    // We can reuse offsets from input if the input owns it. This is only valid
+    // when the first offset is 0, since the output data buffer starts at 0.
     if (input.buffers[1].owner != nullptr) {
       out_arr->buffers[1] = input.GetBuffer(1);
     } else {
diff --git a/cpp/src/arrow/compute/kernels/scalar_string_test.cc b/cpp/src/arrow/compute/kernels/scalar_string_test.cc
index 74650c1d76c..82cd0436631 100644
--- a/cpp/src/arrow/compute/kernels/scalar_string_test.cc
+++ b/cpp/src/arrow/compute/kernels/scalar_string_test.cc
@@ -1176,6 +1176,29 @@ TYPED_TEST(TestStringKernels, AsciiSwapCase) {
                    "[\"HeLLo, wOrLD!\", \"$. a35?\"]");
 }
 
+TYPED_TEST(TestStringKernels, AsciiCaseTransformNonZeroFirstOffset) {
+  // GH-54906: the input is valid even though its first value offset is not 0,
+  // so the kernels must not reuse its offsets buffer as is.
+  auto validity =
+      ArrayFromJSON(boolean(), "[true, false, true, true]")->data()->buffers[1];
+  auto offsets =
+      ArrayFromJSON(this->offset_type(), "[5, 8, 8, 8, 10]")->data()->buffers[1];
+  auto data = Buffer::FromString("xxxxxabCDe");
+  auto input =
+      MakeArray(ArrayData::Make(this->type(), /*length=*/4, {validity, offsets, data}));
+  ASSERT_OK(input->ValidateFull());
+  AssertArraysEqual(*ArrayFromJSON(this->type(), R"(["abC", null, "", "De"])"), *input);
+
+  this->CheckUnary("ascii_upper", input, this->type(), R"(["ABC", null, "", "DE"])");
+  this->CheckUnary("ascii_lower", input, this->type(), R"(["abc", null, "", "de"])");
+  this->CheckUnary("ascii_swapcase", input, this->type(), R"(["ABc", null, "", "dE"])");
+
+  // Slices with a non-zero array offset
+  this->CheckUnary("ascii_upper", input->Slice(1), this->type(), R"([null, "", "DE"])");
+  this->CheckUnary("ascii_lower", input->Slice(2, 1), this->type(), R"([""])");
+  this->CheckUnary("ascii_swapcase", input->Slice(3), this->type(), R"(["dE"])");
+}
+
 TYPED_TEST(TestStringKernels, AsciiCapitalize) {
   this->CheckUnary("ascii_capitalize", "[]", this->type(), "[]");
   this->CheckUnary("ascii_capitalize",