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In the present work, we report the synthesis and evaluation of a graphite-supported bismuth film working electrode (BiFE) in the simultaneous quantification of Hg(II) and Pb(II) at ppb levels. The BiFE was synthesized in-situ by electrodeposition in 1 M HNO3 as the supporting electrolyte at −0.5 V potential. A design of experiments and a response surface model (RSM) were developed to optimize the parameter of bismuth concentration ([Bi]) and deposition time (tdep) in the synthesis of the BiFE. The electrodeposition conditions of [Bi] = 3 mM and tdep = 10s proved to be the optimal conditions for the highest sensitivity and selectivity of the synthesized working electrode. For the quantification of Hg(II) and Pb(II), the electrochemical technique of square wave anodic stripping voltammetry (SWASV) was used by applying a deposition potential of −1 V in 1 M acetic acid buffer solution. The optimization of the factors analyzed in the design of experiments allowed the simultaneous detection of Hg(II) and Pb(II) at limiting levels of 1 ppb and 10 ppb, respectively. The calibration curves of Hg(II) and Pb(II) present an R2 of 0.988 and 0.982, respectively.