In the Fourth Labour Government, as Minister of Agriculture, Moyle oversaw the removal of farming subsidies and the establishment of a fisheries quota system.

In late 1976, Prime Minister Robert Muldoon accused Moyle in Parliament of having been questioned by the police on suspicion of homosexual activities, which were then illegal in New Zealand.

[1] Aged 23 and newly married, Moyle returned to the far north and took over a rough farm in Hokianga next to his parents-in-law's property.

He also augmented his income by winching out "sinkers" (logs of kauri wood) that had disappeared underneath semi-reclaimed mangrove swamps.

He eventually gave up his farm, selling it to his neighbouring father-in-law, as part of an amalgamation deal in order to move to Whangārei for a teaching job.

[2] Moyle joined the Labour Party as a teenager and while still in sixth form was a campaign volunteer for Hugh Watt in the Onehunga electorate.

In 1969 the Mangere electorate was created in the same general area, and Moyle moved his candidacy there, allowing Roger Douglas to take over Manukau.

[10] The government also cut several farming subsidies for pesticides, stock drenches and aerial application of lime and fertiliser a net budget saving of $17.4 million.

He was "enduringly popular with the farming community",[12] and was instrumental in opening up New Zealand's meat trade with the Middle East.

[13] He travelled overseas frequently (often alongside overseas trade minister Joe Walding) to many countries, particularly Iran, Russia and China, to open more export markets for New Zealand's primary produce to replace the diminishing quotas for those products in Britain following their membership of the European Economic Community.

[10] His main goals in the agriculture portfolio was to oversee Labour's campaign commitments to achieve better cost stability for farmers and to convert bulk-commodity-based farming practices to become more market-oriented.

Kirk dismissed the idea, concerned that it would increase inflation, which Moyle acknowledged but thought that inflationary impacts would be less than the returns on stimulated economic growth.

According to political commentator Bruce Jesson, Moyle was the preferred candidate due to his strong performance as Minister of Agriculture.

[21] The Prime Minister then alleged that Moyle had been questioned by the police on suspicion of homosexual activities (which were then illegal) in Wellington.

"[18] The so-called 'Moyle Affair' dominated the newspaper headlines, and became a rallying point for the nascent gay liberation movement in New Zealand, which bemoaned that the mere accusation of homosexuality could end a career.

[23] Initially Moyle intended to stand for re-election to vindicate himself of the allegations, but withdrew his name from the nominations only three days before the selection meeting.

[24] Ironically, the subsequent 1977 by-election was won by David Lange, and the attention that this got him helped propel him to the leadership of the Labour Party and his landslide victory over Muldoon in the 1984 election.

[13] Moyle then turned his attention to nominating for the nearby seat of Papatoetoe, which was newly created and incorporated parts of Mangere.

As one of the few Labour MPs with Ministerial experience, Moyle was reappointed to Cabinet, again holding the portfolios of Agriculture and Fisheries (now separate departments) and regaining charge of the Rural Banking and Finance Corporation.

Driven by Finance Minister Roger Douglas, it embarked on a programme, known as Rogernomics, aimed at deregulating the economy.

[34] This included the Rural Banking and Finance Corporation which Moyle had established ten years earlier, which Douglas sold to private enterprise.

[38] He also supported the New Zealand Wool Board in its expansion into conducting commercial activities, albeit whilst continuing with their regulatory functions as well.

[13] In the 1990 Queen's Birthday Honours, Moyle was appointed a Commander of the Order of the British Empire, for public services.

[42] Moyle retired to a 300-hectare (740-acre) sheep and cattle farm at Waimate North in the Bay of Islands with his wife Millicent and son Greg, who was his co-farmer.