In 1955, when the federal Labor leader, H. V. Evatt, attacked the Groupers and brought on a major split in the Labor Party, Cairns sided with Evatt. At the 1955 election, he stood for the House of Representatives for the working-class seat of Yarra, held by the leading Grouper, Stan Keon. In what Cairns has been quoted as saying was "... the most active and intense and vigorous election campaign that's ever been run in Australia", Cairns was elected and held Yarra until 1969, when it was abolished at a redistribution. He then shifted to Lalor in Melbourne's western suburbs. The seat had been in Labor hands since its creation in 1949, but had been taken by Liberal Mervyn Lee in 1966, as part of that year's pro-Liberal landslide. However, a redistribution wiped out Lee's majority and gave Labor a notional majority of six per cent. Rather than face almost certain defeat, Lee made an unsuccessful bid for the seat of Bendigo. This proved prescient, as Cairns easily won Lalor with a healthy swing.