In this study, an electrochemical sensor for the sensitive determination of dopamine was developed based on pencil graphite electrodes (PGEs) modified by two different approaches. In the first approach, the polydopamine (PDA)-coated PGEs (PDA@PGE) were decorated with the as-prepared citrate-stabilized gold or silver nanoparticles (cit-AuNPs and cit-AgNPs, respectively). In the second approach, similarly, PDA@PGE was decorated with metallic NPs by reducing silver (r-AgNPs) or gold ions (r-AuNPs). In this process, PDA with its numerous functional groups such as catechol and amine plays an essential role in both the reduction of the metallic ions and the adsorption and stabilization of the NPs. The characterization of the modified electrodes was examined by field-emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, ultraviolet-visible absorption spectra, and cyclic voltammetry. These observations depicted that the density of NPs could be manipulated over time, and 3 h of NPs deposition time was detected as optimal via electrochemical analysis. The PDA@PGEs decorated with AuNPs were also used for the electrochemical analysis of dopamine in calibration and validation studies. In the analysis of dopamine by the square wave voltammetry method, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.53 and 1.77 mu M, respectively. For the differential pulse voltammetry, LOD and LOQ were 0.96 and 3.2 mu M, respectively. We observed that the PDA-coated PGEs decorated with AuNPs provided high accuracy, precision, reproducibility, and reliability. The experimental results were found to be insignificant at a 95% confidence level. The developed sensor was applied for the determination of dopamine in biological fluids.