As tensions with the mother country escalated, in 1773 Cary served as a member of Virginia's committee of correspondence. When the House of Burgesses was dissolved at the outset of the American Revolution, he served as a delegate to the Virginia Conventions. At the Fifth Virginia Convention in May 1776, he served as the chairman of the committee of the whole that adopted the celebrated resolution of independence, which instructed Virginia's delegates to the Second Continental Congress to propose a declaration of independence. After Virginia became an independent state in 1776, Cary became the first speaker of the Senate of Virginia, and remained in that position until his death.