The crystal plasticity finite element (CPFE) method was used to predict forming limit strains of hexagonal close‒packed (HCP) polycrystalline magnesium alloy sheets, namely AZ31 and ZE10, under an isothermal temperature condition. The strain rate‒dependent uniaxial tensile test data along various loading directions and an initial texture were used to determine the constitutive parameters of the crystal plasticity model. A hybrid representative volume element approach, which combines the CPFE and the Marciniak–Kuczynski model, was developed to obtain the forming limit diagram of the magnesium alloys. The predicted forming limits were in excellent agreement with the Nakazima test results. Moreover, the microscopic responses such as slip/twin activation and deformation texture changes during various loading paths from uniaxial tension to the balanced biaxial tension were comprehensively analyzed and discussed from the CPFE results to understand the underlying micro‒mechanism for the macro‒mechanical responses.