An Act of Parliament declaring England a Commonwealth is passed by the Long Parliament. England would be a republic for the next eleven years.

An act of parliament, as a form of primary legislation, is a text of law passed by the legislative body of a jurisdiction. In most countries with a parliamentary system of government, acts of parliament begin as a bill, which the legislature votes on. Depending on the structure of government, this text may then be subject to assent or approval from the executive branch.