This paper proposes a class of velocity-free attitude stable controller using a novel finite-time observer for spacecraft attitude tracking, which explicitly takes into account control input saturation to assure fast and accurate response and to achieve effective compensation to the effect of external disturbance as well. First, a novel semiglobal finite-time convergent observer is proposed to estimate the angular velocity in a finite-time under external disturbance. Then, a simple global output feedback controller is proposed by adoption of the designed finite-time observer. Rigorous proofs show that the proposed observer can achieve the finite-time stability and the controller rigorously enforces actuator magnitude constraints. Numerical simulations illustrate the spacecraft performance obtained using the proposed controller.