The formation of high-nuclearity silver(I) clusters remains elusive and their potential applications are still underdeveloped. Herein, we firstly prepared a chain-like thiolated Ag complex {[Ag (S Bu) (NO ) (CH CN) (H O) ] ⋅ [Ag (S Bu) (NO ) (CH CN) ]} (abbreviated as Ag ) in which two similar Ag clusters are assembled by NO anions. The solution containing Ag reacted with hydrogen sulfide with controlled concentration, promptly producing another identifiable and bright red-emitting high-nuclearity silver(I) cluster, Ag (S) (S Bu) (NO ) (abbreviated as Ag ). We tracked the transformation using time-dependent electrospray ionization mass spectrometry (ESI-MS), UV/Vis absorption and photoluminescence spectra. Based on this cluster transformation, we further developed an ultra-sensitive turn-on sensor detecting H S gas with an ultrafast response time (30 s) at a low detection limit (0.13 ppm). This work opens a new way of understanding the growth of metal clusters and developing their luminescent sensing applications.