Cyclic voltammetry and spectroelectrochemistry (e.p.r.) were used to investigate the mechanisms implied in the electrocarboxylation of chloroacetonitrile (Cl-CH2-CN, noted RCl) mediated by [Ni(II)(terpy)2]2+. The oxidative addition of chloroacetonitrile on the electrogenerated [Ni(I)(terpy)]+ yields an alkyl-nickel R-Ni(III) complex which is reduced into an alkyl-nickel(II). E.p.r study shows that the homolytic nickel-carbon bond cleavage seems to be the more probable pathway to form the organic radical R-which is reduced to R−. Under carbon dioxide atmosphere, cyclic voltammetry studies show that CO2 was added on the alkyl-Ni(III) complex giving probably a CO2 adduct which is reduced to RCO2-Ni(II) complex allowing to release the carboxylate RCO2− and the active [Ni(I)(terpy)]+ complex. Controlled potential electrolyses showed that good carboxylated and faradic yields were obtained.