The metallation reaction of 2-[2-(3,5-dibutoxycarbonylphenoxy)ethoxy]ethylsulfanyl-substituted porphyrazine with manganese and nickel salts led to novel porhyrazine derivatives with d-block metal ions in the core. Voltammetric studies of nickel(II) porphyrazine in organic electrolyte revealed the existence of well-defined one-electron ligand-based reductions and ligand-based one-electron oxidation redox pairs. Manganese porphyrazine however, presented both metal-based and ligand-based reductions and oxidation processes. The glassy carbon electrode with deposited single-walled carbon nanotube/sulfanyl porphyrazine hybrids was examined for the electrocatalytic oxidation of nitrites. The results indicated that when nickel(II) porphyrazine is present, it significantly contributes to the promotion of the electrocatalytic current for nitrites oxidation. The response of the proposed modified electrode was linear considering the nitrites concentration in the range of 5–200 μM and with a detection limit (LOD) and quantitation limit (LOQ) equal to 1.08 and 3.60 μM, respectively. The proposed voltammetric sensor was also applied for the determination of nitrites in tap water and mineral water samples.