Experimental data on cycles to failure are reported for a SCS-6/TIMETAL 21S [0/90]^s composite under isothermal fatigue at 650 and 815°C over a range of frequencies from 0.01 to 200 Hz as well as under in-phase and out-of-phase thermomechanical fatigue from 150 to 650°C. Several models are evaluated for correlating fatigue lives based on computed micromechanical stresses using a life fraction concept that considers both cycle-dependent and time-dependent terms. Fractography is used to illustrate the range of failure modes in this material system as well as to both guide and validate the modeling concepts. Over the range of conditions covered in this investigation, purely time-dependent, purely cycle-dependent, fiber-dominated, and matrix-dominated modes of failure, as well as combinations of these, are observed.