In this paper, a hydrothermal technique was applied for the synthesis of glucose-treated reduced graphene oxide (GTRGO). Bismuth (Bi) was electrochemically deposited on the modified GTRGO surface for highly sensitive heavy-metal-ion-sensor applications. The fabricated electrode was then characterized for the detection of lead and cadmium heavy-metal ions in an acetic-acid-buffered solution using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated electrode exhibited a linear detection range of 1.0 μg L−1 to 100.0 μg L−1 for both of the ions, and detection limits of 0.4 μg L−1 and 1.0 μg L−1 were obtained for the lead and cadmium (S/N = 3), respectively. These results show that the proposed GTRGO material is highly promising for the production of a highly sensitive, stable, and reliable electrochemical sensor.