In 1940, Holland replaced National's first non-interim leader Adam Hamilton as the leader of the National Party. Prior to becoming the Party's leader, he had served as Hamilton's parliamentary secretary. As leader of the National Party, Holland sought to win the support of the party's farming constituency by establishing a farm in North Canterbury and breeding Romney sheep and Aberdeen Angus cattle. In addition, he also countered other rival conservative parties like the Liberal Party, the Soldier's Movement, and the People's Movement by co-opting them into the National Party in 1941. This merger helped strengthen National's support base by unifying opposition to the Labour Party. Holland served as Leader of the Opposition for nearly ten years until the National Party won the 1949 general election. He represented the Christchurch North electorate from 1935 to 1946, and then the Fendalton electorate from 1946 to 1957.