During the Labor Party's internal tensions in the 1930s, McKell came to be seen as a compromise candidate for the leadership of the party. He replaced Jack Lang as leader of the opposition in 1939, and became premier following Labor's victory at the 1941 state election. As premier, McKell oversaw both the war effort and the initial stages of post-war reconstruction, carrying out an ambitious programme of public works as well as various social reforms. He was re-elected with an increased majority at the 1944 election, making him the first Labor premier to win successive elections in New South Wales.