Methyl nicotinate (MN) is an important tuberculosis biomarker, and can be effectively measured using electrochemical methods. In this study, we have developed a novel N-doped phenolic polymer nanocomposite in situ dispersed with reduced graphene oxide and cobalt (Co)-nanoparticles as a sensor electrode (Co-rGO/PC). Co-nanoparticles were used for the MN recognition. Carbonization was performed for the reduction of GO and the synthesis of Co-nanoparticles. The prepared electrode materials were characterized using SEM, EDS, EIS, and CV. Tested using differential pulse voltammetry, Co-rGO/PC showed its pplicability (RSD < 6%) over 0.05–20.0 mg L−1 MN concentration with high sensitivity (S/N ratio = 3). The present method and materials can also be used for the development of sensors for the other biomarkers.