In 1627, Rich was involved in the disastrous Siege of Saint-Martin-de-Ré, which led to Buckingham's impeachment by Parliament; although this failed, he was assassinated on 23 August 1628. The next day, Rich wrote to Charles claiming he had been promised the position Governor of Windsor Castle. This request was granted, along with an appointment as Governor of Landguard Fort, and he benefited from his relationship with Henrietta Maria, who had replaced Buckingham as Charles' closest advisor. Over the next few months, he was made Lord Lieutenant of Berkshire and Middlesex, Chancellor of the University of Cambridge, and numerous other offices.