Functional group exchanges based on single-bond transformation are rare and challenging. In this regard, functional group exchange reactions of hydrosilanes proved to be more problematic. This is because this exchange requires the cleavage of the C–Si bond, while the Si–H bond is relatively easily activated for hydrosilanes. Herein, we report the first Si–B functional group exchange reactions of hydrosilanes with hydroboranes simply enabled by BH₃ as a catalyst. Our methodology works for various aryl and alkyl hydrosilanes and different hydroboranes with the tolerance of general functional groups (up to 115 examples). Control experiments and density functional theory (DFT) studies reveal a distinct reaction pathway that involves consecutive C–Si/B–H and C–B/B–H σ-bond metathesis. Further investigations of using more readily available chlorosilanes, siloxane, fluorosilane, and silylborane for Si–B functional group exchanges, Ge–B functional group exchanges, and depolymerizative Si–B exchanges of polysilanes are also demonstrated. Moreover, the regeneration of MeSiH₃ from polymethylhydrosiloxane (PMHS) is achieved. Notably, the formal hydrosilylation of a wide range of alkenes with SiH₄ and MeSiH₃ to selectively produce (chiral)trihydrosilanes and (methyl)dihydrosilanes is realized using inexpensive and readily available PhSiH₃ and PhSiH₂Me as gaseous SiH₄ and MeSiH₃ surrogates.