He was Lord High Commissioner to the General Assembly of the Church of Scotland, a Privy Councillor and one of the Committee of the Estates. Wemyss later supported the Parliament of Scotland against Charles I in the Wars of the Three Kingdoms, and died in 1649. He married Jane Gray (daughter of Patrick Gray and his second wife, Mary Stewart, daughter of Robert Stewart, 1st Earl of Orkney, the King's uncle) and was succeeded by his only son, David, the second Earl.