Observing and controlling macroscopic quantum systems has long been a driving force in research on quantum physics. In this endeavor, strong coupling between individual quantum systems and mechanical oscillators is being actively pursued [1-3]. While both read-out of mechanical motion using coherent control of spin systems [4-9] and single spin read-out using pristine oscillators have been demonstrated [10, 11], temperature control of the motion of a macroscopic object using long-lived electronic spins has not been reported. Here, we observe both a spin-dependent torque and spin-cooling of the motion of a trapped microdiamond. Using a combination of microwave and laser excitation enables the spin of nitrogen-vacancy centers to act on the diamond orientation and to cool the diamond libration via a dynamical back-action. Further, driving the system in the non-linear regime, we demonstrate bistability and self-sustained coherent oscillations stimulated by the spin-mechanical coupling, which o↵ers prospects for spin-driven generation of non-classical states of motion. Such a levitating diamond operated as a compass with controlled dissipation has implications in high-precision torque sensing [12-14], emulation of the spin-boson problem [15] and probing of quantum phase transitions [16]. In the single spin limit [17] and employing ultra-pure nano-diamonds, it will allow quantum non-demolition read-out of the spin of nitrogen-vacancy centers under ambient conditions, deterministic entanglement between distant individual spins [18] and matter-wave interferometry [16, 19, 20].