diff --git a/c_glib/arrow-glib/decimal.cpp b/c_glib/arrow-glib/decimal.cpp
index 04787aba47c89..9c0cf03607a84 100644
--- a/c_glib/arrow-glib/decimal.cpp
+++ b/c_glib/arrow-glib/decimal.cpp
@@ -202,6 +202,21 @@ garrow_decimal128_negate(GArrowDecimal128 *decimal)
   arrow_decimal->Negate();
 }
 
+/**
+ * garrow_decimal128_to_integer:
+ * @decimal: A #GArrowDecimal128.
+ *
+ * Returns: The 64-bit integer representation of the decimal.
+ *
+ * Since: 0.10.0
+ */
+gint64
+garrow_decimal128_to_integer(GArrowDecimal128 *decimal)
+{
+  auto arrow_decimal = garrow_decimal128_get_raw(decimal);
+  return static_cast<int64_t>(*arrow_decimal);
+}
+
 G_END_DECLS
 
 GArrowDecimal128 *
diff --git a/c_glib/arrow-glib/decimal.h b/c_glib/arrow-glib/decimal.h
index 90cb247bc9e6f..ba9e18df2bf33 100644
--- a/c_glib/arrow-glib/decimal.h
+++ b/c_glib/arrow-glib/decimal.h
@@ -42,5 +42,6 @@ gchar *garrow_decimal128_to_string_scale(GArrowDecimal128 *decimal,
 gchar *garrow_decimal128_to_string(GArrowDecimal128 *decimal);
 void garrow_decimal128_abs(GArrowDecimal128 *decimal);
 void garrow_decimal128_negate(GArrowDecimal128 *decimal);
+gint64 garrow_decimal128_to_integer(GArrowDecimal128 *decimal);
 
 G_END_DECLS
diff --git a/c_glib/test/test-decimal.rb b/c_glib/test/test-decimal.rb
index 03e88cfc3cb80..2528883233b9b 100644
--- a/c_glib/test/test-decimal.rb
+++ b/c_glib/test/test-decimal.rb
@@ -46,4 +46,10 @@ def test_negate
     decimal.negate
     assert_equal(positive_value, decimal.to_s)
   end
+
+  def test_to_integer
+    integer_data = 999999999999999999
+    decimal = Arrow::Decimal128.new(integer_data)
+    assert_equal(integer_data, decimal.to_i)
+  end
 end