A flexible, transparent, single-walled carbon nanotube (SWCNT) film electrode was prepared by vacuum filtering methods, followed by photolithographic patterning of a photoresist polymer on the SWCNT surface. The morphology of the SWCNT film electrode surface was characterized using a field-emission scanning electron microscope coupled to an energy-dispersive X-ray spectrophotometer. The electrodes were successfully used as a mercury-free electrochemical sensor for individual and simultaneous detection of cadmium (Cd2+) and lead (Pb2+) in 0.02 M HCl by square-wave stripping voltammetry. Some important operational parameters, including deposition time, deposition potential, square-wave amplitude, and square wave-frequency were optimized for the detection of Cd2+ and Pb2+. The newly developed sensor showed good linear behavior in the examined concentration. For individual Cd2+ and Pb2+ ion detection, the linear range was found from 0.033 to 0.228 ppm with detection limits of 0.7 ppb (R2 = 0.985) for Cd2+ and 0.8 ppb (R2 = 0.999) for Pb2+. For simultaneous detection, the linear range was found from 0.033 to 0.280 ppm with a limit of detection of 2.2 ppb (R2 = 0.976) and 0.6 ppb (R2 = 0.996) for Cd2+ and Pb2+, respectively. SWCNT film electrodes offered favorable reproducibility of ±5.4% and 4.3% for Cd2+ and Pb2+, respectively. The experiments demonstrated the applicability of carbon nanotubes, specifically in the preparation of SWCNT films. The results suggest that the proposed flexible SWCNT film electrodes can be applied as simple, efficient, cost-effective, and/or disposable electrodes for simultaneous detection of heavy metal ions.