Born in Grafton, New South Wales, he was educated at St Augustine's School in Coffs Harbour.

In 1958, he was the Labor candidate for the seat of Cowper in the Australian House of Representatives, facing former caretaker Prime Minister Earle Page of the Country Party.

On the second count, while an independent candidate's preferences flowed mostly to Page, McGuren's first-count lead was large enough for him to be elected by a slim three-point margin – a 13-point swing to the ALP, and one of the largest upsets in Australian political history.

McGuren's win was part of a 15-seat swing to Labor which almost brought down the government of Sir Robert Menzies.

At the 1963 election, he was narrowly defeated by the Country Party's Ian Robinson on the first count, as the Menzies-led Coalition recovered many of the seats it had lost two years earlier.