We have developed photoboosted stannylation reactions of terminal alkynes (linear-selective hydrostannylation) and fluoroarenes (defluorostannylation), in which the stannyl anion is photoexcited to an excited triplet (T1) stannyl diradical species. This unprecedented T1-stannyl diradical species shows completely different reactivity and selectivity from those of stannyl anions and stannyl radicals. This methodology is operationally simple, has broad functional group tolerance, and proceeds in high yield without the need for any catalyst.