Nitrate fertilizer runoff poses chemical challenge for their remedial as relatively inert nitrate-oxoanions require stringent conditions for reduction. We present a novel strategy of using thiols RSH that represent biologically relevant reductants to convert nitrate to NO at a Cu(II) center under mild conditions with formation of disulfides RSSR. The bidentate b-diketiminato complex [Cl2NNF6]Cu(κ2-O2NO) engages in O-atom transfer (OAT) with various thiols (RSH) to form sulfenic acid (RSOH). Mechanistic studies indicate formation of the copper(II) nitrite complex [Cl2NNF6]Cu(κ2-O2N) upon OAT that further reacts with RSH to give S-nitrosothiols RSNO and [CuII]2(m-OH)2 en route to NO formation with [CuII]-SR intermediates. H2S, a physiologically potent agent and thiol congener, also reduces nitrate at copper(II) to NO generation, providing a lens into NO3-/H2S cross-talk in the biological milieu.