In this study, sulfur-enriched microporous organic polymer (MOP) was prepared using one-pot Shiff-base type polycondensation reaction of thiophendicarboxaldehyde with melamine. With 195.731 m2 g−1 surface area and 0.047 cm3 g−1 pore volume, the as-synthesized MOP has a cotton-like morphology and a micropore-dominated pore size distribution. After loading MOP with nickel as a co-catalyst, we demonstrated that the obtained framework could be used as an efficient and robust electrocatalyst for hydrogen evolution reaction (HER) in an alkaline medium with the optimum composite (Ni2@MOP) exhibiting a low onset potential of −66 mV. Furthermore, the optimum electrocatalyst showed good stability, delivering 91% faradaic efficiency (FE) after a 3.5 h chronoamperometry experiment.