This paper is focused on the development of viable cruciform-shaped specimen geometries where large biaxial plastic deformation can be achieved within their gauge areas. A custom-built balanced biaxial testing fixture is used to plastically deform a variety of carefully-designed AZ31B-H24 magnesium specimens until failure. Images recorded from a digital camera positioned to monitor deformation in the gauge area of each specimen are used to compute the strain fields with a digital image correlation (DIC) algorithm. The viability of each design is validated based on the extent of biaxiality of measured strains and its ability to promote plastic deformation within its gauge area up until failure. The study provides key insights into the influences of certain geometrical parameters on deformation-biaxiality in cruciform specimens.