When, in 1984, the Labour Party won the general elections, Palmer became Deputy Prime Minister of the Fourth Labour Government. He also became Attorney-General and Minister of Justice. The new justice minister, who had promoted proportional representation as a law professor in his book "Unbridled Power?", also published in 1984, set up a Royal Commission to investigate the electoral system and propose modifications or alternatives. His Royal Commission reported in December 1986, recommending the mixed-member proportional representation system. After the 1987 elections, when Labour was re-elected, he also became Minister of the Environment, an area in which he took personal interest.