The mechanical behaviour of Mg65−xLixCu25Y10 (x = 9, 14 and 19) metallic glass composites has been studied. For 9 and 14 at.% Li the alloys exhibit a brittle behaviour. The microstructure of the alloy containing 9 at.% Li consists of a bcc Mg-Li solid solution phase embedded in an amorphous phase. Higher concentrations of Li promote the formation of the bcc phase, Mg2Cu and also a small volume fraction of Y-containing intermetallic. The alloy with the highest Li content, i.e. 19 at.%, exhibits a compressive engineering strain of 25%. The hierarchical microstructure design with multiphase components allows for the operation and interaction of different deformation behaviour to provide for useful levels of plastic deformation.