Lead halide perovskite nanocrystals in a glass matrix are a promising platform for optoelectronic applications due to their excellent optical properties combined with outstanding stability against the environment. We reveal the potential of this system for spintronics by studying the electron spin properties of CsPb(Cl,Br) 3 nanocrystals in a fluorophosphate glass matrix. Using optical spin orientation and spin depolarization with a radio frequency field, we measure longitudinal spin relaxation time, T 1 , reaching several hundreds of microseconds at low temperatures. This time T 1 corresponds to a spin state with a small g factor, which we attribute to a weakly exchangecoupled electron−hole pair with antiparallel spins.