When the First English Civil War began in August 1642, Rich remained in London rather than joining the Royalists. He defected in July 1643 after failing to persuade his cousin and Parliamentarian commander Robert Devereux, 3rd Earl of Essex to negotiate peace terms. He switched sides again and returned to London in December, narrowly avoiding being tried for treason. After talks between Charles and Parliament broke down in late 1647, he took part in the 1648 Second English Civil War as a Royalist; captured in July, he was executed in March 1649.