Repetitive hot rolling followed by hot pressing or hybrid severe plastic deformation (HSPD) of Mg-4Zn-4Gd was performed at 450 °C to produce ultrafine-grains (UFG) in the alloy. The processed specimens are compared with conventional 75% hot rolled, solutionized (ST) and as-cast (AC) specimens to study the mechanical and microstructural evolution. Prior to HSPD process, the pre-processed blocks were solutionized at 400 °C for 24 h to obtain the equiaxed and residual stress free alloy for easy plastic deformation up to the high absolute true strain value of 1.39. The hot rolling (R) and hot pressing (P) methods were combined to deform the material in three different combinations in terms of true strains to achieve the final deformation with true strain 1.39 (75% reduction). The HSPDed specimens were subjected to tensile, hardness and fracture toughness (KQ and JⅠC) tests. The 50R50P specimen has shown better improvement in yield strength (σYS = 268 MPa), tensile strength (σTS = 284 MPa)), and hardness (2.21 GPa) amongst other HSPDed specimen. The improvement in mechanical properties of 50R50P alloy is nearly 9%, 6.5%, and 81%, respectively over the 75% rolled specimen and 154%, 65%, and 176%, respectively against ST specimens. However, the elongation of 50R50P specimen has improved only up to ~ 27% than ST specimen. The highest JⅠC fracture toughness of the processed alloy is ~ 23.25 kJ/m2 when pre-crack is normal to rolling direction (RD) and ~ 18.51 kJ/m2 when pre-crack is parallel to RD analysed in 50R50P and 70R16P specimens, respectively. The strengthening mechanisms operating in the processed alloy is due to solid solution strengthening and deformation slip based failure mechanism in fine grained alloys, which were elucidated with the help of high resolution transmission electron microscopy (HRTEM). The HRTEM results are correlated with X-ray diffraction results of processed alloy. Fracture phenomena for different HSPDed specimens were analysed through FE-SEM to understand the failure characteristics of the alloy under static load.