[2] Having struggled sporadically with obesity and occupational burnout throughout his life, from 1974 Kirk suddenly developed difficulty in breathing, eating and sleeping, which rapidly got worse.

Kirk ignored advice from several doctors and from Bob Tizard and Warren Freer to "take care of himself" and to reduce his heavy consumption of Coca-Cola and alcohol (beer, plus later whisky or gin), saying he would have a "short but happy life".

His final public appearance was on 18 August to open St Peter's Catholic College in Palmerston North, when he stood in the rain for the whole ceremony, and he missed a proposed debate with Robert Muldoon before interviewer David Frost.

He had been checked over by many doctors, and an examination by Professor Tom O’Donnell on 27 August confirmed that he had an enlarged heart gravely weakened by embolisms, and which was not pumping regularly enough to get sufficient oxygen into his bloodstream; one lung was two-thirds incapacitated by the clot; and his stomach was very sore as his liver was swollen with retained fluid.

Harold Wilson, Gough Whitlam, Gerald Ford, Henry Kissinger and Pierre Trudeau all paid tribute to the loss of Kirk.

British Foreign Secretary James Callaghan said Kirk was a "loyal friend of this country, an outstanding leader of the New Zealand Labour Party, and a strong believer in Commonwealth ties.

He stated "Although we differed in our political views I admired his common-sense approach to world problems as well as his single-mindedness of purpose in looking after the interests of his own country.

French Minister of Foreign Affairs, Jean Sauvagnargues, wrote "I have learned with great sadness the news of the death of Mr Kirk.

"[10] Politician and historian Michael Bassett has described Kirk as 'Labour’s last passionate believer in big government, someone whose commanding presence and extravagant rhetoric introduced a new idealism to political debate in New Zealand'.

[12] The parliamentary opposition stated they would refrain from all political activity until after the Labour Party caucus met to select a new Prime Minister.

The Leader of the Opposition, Robert Muldoon, said that the National Party would "not raise issues or pursue arguments that might in any way be divisive within the Government caucus, which might cloud the judgment of its members.