He entered Parliament as a National Party MP in 1969 and served as a cabinet minister from 1975 to 1980, when he resigned to become New Zealand's Ambassador to the United States.

[8][2] In 1972, Gill supported Robert Muldoon's candidacy to succeed Keith Holyoake as the leader of the National Party, which was ultimately won by Jack Marshall.

According to the historian Barry Gustafson, Gill had a tense relationship with Prime Minister Muldoon, with the two disagreeing strongly on several occasions.

[22][23] As Minister of Immigration, Gill supported the Government's dawn raids against overstayers, which disproportionately targeted the Pasifika community.

In response the Polynesian Panthers activist group staged "counter raids" on the homes of Gill and fellow National MP and minister Bill Birch, surrounding them with light and chanting with megaphones.

[29] While serving as Ambassador to the United States, Gill was hospitalised at Georgetown University Hospital on 16 February 1982 and returned to New Zealand on a stretcher[4] shortly before his death in Auckland on 1 March 1982.

His ashes were buried in the Royal New Zealand Returned and Services' Association section at North Shore Memorial Park.