The Leader of the Opposition (sometimes known as the Leader of the Opposition in the House of Commons) in the United Kingdom is the politician who leads Her Majesty's Most Loyal Opposition. There is also a Leader of the Opposition in the House of Lords. At one time the leaders in the two Houses were of equal status, unless one was the most recent Prime Minister from the party forming the official opposition. However since early in the twentieth century there has been little dispute that the leader in the House of Commons was pre-eminent.

The Leader of the Opposition is normally the leader of the largest party not within the government, which is usually the second largest party in the House of Commons. He or she is normally viewed as an alternative Prime Minister, and is a member of the Privy Council.

The current Leader of the Opposition is David Cameron, leader of the Conservative Party.