In 1999 Coltart was asked to join the Movement for Democratic Change (MDC) by trade union leader Morgan Tsvangirai who appointed him interim Legal Secretary for the party. In January 2000, at the inaugural congress of the MDC, Coltart was elected Secretary for Legal Affairs. This position gave him the responsibility of formulating the MDC justice policy, of conducting the MDC's electoral court challenges and of organising the legal defence of MDC members who had been detained and prosecuted, including Morgan Tsvangirai's treason trial.