Leslie took an active part with the Lords of the Congregation, first against the queen-mother, Mary of Guise, when she was regent of Scotland, and afterwards against Mary, Queen of Scots in opposing her marriage with Lord Darnley, and in being part of the plot to murder David Rizzio. He was, however, one of the peers who acquitted Bothwell of Darnley's murder, and went over to the side of the queen. He fought for her at the Battle of Langside, and continued to occupy a position of some prominence in Scottish affairs until his death in 1611.