The United Australia Party or UAP was an Australian political party that was the political successor to the Nationalist Party of Australia. It was formed in 1931 when Joseph Lyons, a Labor MP, and his supporters crossed the floor to bring down the Scullin Labor Government.

The UAP won the subsequent parliamentary elections, and Lyons became Prime Minister. After 1934 the UAP governed in coalition with the Country Party of Earle Page. By 1939, serious leadership ructions had begun to emerge in the UAP. The ambitious Deputy Leader Robert Menzies sought to keep Lyons to his promise to resign in his favour. Menzies did not have widespread support, particularly from the Country Party, and various plots were made to advance former Prime Ministers Billy Hughes or Stanley Bruce to the leadership of the UAP. Menzies resigned as Deputy Leader, and less than a month later, in April, Lyons died.

When Menzies narrowly defeated Hughes to be elected as UAP leader, Page withdrew the Country Party from the Coalition. The coalition was reformed under new Country Party leader Archie Cameron in March 1940. Continuing problems with the administration of the war effort and the undermining of his leadership by a group that were described by Arthur Coles as "the UAP lynch-mob", led Menzies to resign as party leader and Prime Minister in August 1941, and the UAP then elected the frail 79-year-old Hughes as their new leader. He was replaced again by Menzies in 1943.

The UAP became politically irrelevant following its massive defeat in the 1943 Federal election. The UAP was absorbed into the Liberal Party of Australia at the founding of the latter organization on 31 August 1945. The Liberal Party of Australia went on become the dominant right wing party in Australian politics.

Leaders

• Joseph Lyons 1931-1939
• Robert Menzies 1939-1941
• William Morris Hughes 1941-1943
• Robert Menzies 1943-1945