mcgirr was first elected to the new south wales legislative assembly in 1922 and served continuously until 1952, holding the various seats of cootamundra, cumberland, bankstown, and liverpool. having served in the third ministry of jack lang, and the first and second ministries of william mckell, mcgirr was variously torn between lang labor and the newly formed australian labor party. when mckell stood aside as premier in 1947 in order to take up an appointment as governor-general of australia, mcgirr was elected labor leader and became premier.