This paper investigates the cyclic deformation behavior of powder metallurgy alloy FGH96 under multiaxial fatigue loading at 650 °C. The experimental results indicate that different loading paths significantly affect the fatigue life. By analyzing the evolution of stress peaks under different phase angle conditions, it was found that FGH96 exhibits cyclic hardening or cyclic softening behaviors under different loading conditions. The cyclic deformation behavior changes with variations in the mechanical phase angle. Additionally, non-proportional additional hardening increases the stress peak response, which is a key factor affecting fatigue life.