The reaction of the N-heterocyclic-carbene-stabilized disilicon(0) complex [IPr→Si═Si←IPr] (1; IPr = :C{N(Ar)CH}2 and Ar = 2,6-iPr2C6H3) with ArN3 afforded the N-heterocyclic-carbene-stabilized siladiimide [ArNSi(IPr)NAr] (2). X-ray crystallography and theoretical studies show that the N–Si–N skeleton in compound 2 possesses considerable double-bond character and the Si atom is stabilized by the N-heterocyclic carbene.