An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C–H activation mediated by the germylene (germanediyl) Ge(ArMe6)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2) showed that it proceeded by initial MeNC adduct formation followed by an isomerization involving the migratory insertion of the MeNC carbon into the Ge–C ligand bond. Addition of excess MeNC led to sequential insertions of two further MeNC molecules into the Ge–C bond. The insertion of the third MeNC leads to methylisocyanide methyl group C–H activation to afford an azagermacyclopentadienyl species. The X-ray crystal structures of the 1:1 (ArMe6)2GeCNMe adduct, the first and final insertion products (ArMe6)tiebar above startGeC(tiebar above endNMe)ArMe6 and (ArMe6)tiebar above startGeC(NHMe)C(NMe)C(ArMe6)tiebar above endNMe were obtained. The DFT calculations on the reaction pathways represent the first detailed mechanistic study of isocyanide oligomerization by a p-block element species.