Buckling-restrained braces with mass timber restrainers (MT-BRBs) have recently been investigated by several researchers. However, timber restrainers exhibit brittle failure modes and have lower stiffness and strength than their composite and steel counterparts. Previous experiments have demonstrated that timber restrainers are particularly susceptible to local bulging and that this is a brittle failure resulting in a near total loss of strength. Nevertheless, local bulging and global stability design methods have not yet been established for BRBs with timber restrainers. This paper presents cyclic loading tests of MT-BRBs featuring different bolted restrainer compositions, core plate clearances, reinforcing plate arrangements, connections and boundary conditions. These tests produced a variety of weak- and strong-axis bulging and global buckling failure modes. Design methods were developed to prevent each failure mode and then used to design full-scale MT-BRBs that were successfully tested and exhibited excellent performance.