When only 25 years old Egerton became state secretary of the Queensland Boilermakers Union, and well before reaching the age of 40 he had become one of the leading figures in Queensland politics, as Vince Gair (ALP Premier since 1952) found to his cost in 1957. In addition to being president of the Queensland Trades and Labor Council from 1967 to 1976, Egerton served as president of the Australian Labor Party state executive for much of the same period (1968–76). Meanwhile, he held high rank in the Australian Council of Trade Unions and was a member of the ALP's federal executive.
During the 1970s, Egerton acted as Prime Minister Gough Whitlam's right-hand man in Queensland and frequently clashed with the state's conservative Premier Joh Bjelke-Petersen. Subsequently he fell out with Whitlam, the results of this quarrel being dramatic and unexpected on all sides.
In 1976 Egerton became the Australian Labor Party's first and only knight for a quarter of a century (by contrast, the analogous New Zealand party had, and still has, several knights in its ranks). William McKell, who during the 1940s had been Premier of New South Wales, had accepted a knighthood in 1951, but only after leaving the ALP and being appointed Governor-General.
Exactly why Egerton broke with ALP tradition and accepted the honour was a question that he never publicly answered. It is said that the only man who knew the secret was former Senator Albert Patrick Field, but Field committed suicide in 1990 without revealing anything about the subject.
Malcolm Fraser, who had defeated Whitlam in a landslide at the December 1975 federal election, offered the knighthood to Egerton for service to the trade union movement. The award cost Egerton his ALP membership, and earned him the name of 'Jumping Jack the Black Knight', as well as prompting in some quarters the even more hostile epithet 'Labor Rat'. By odd coincidence, Egerton, the son of a boilermaker, received his knighthood from Governor-General John Kerr, also the son of a boilermaker. An outraged Whitlam would later say the knighthood was "the most inappropriate conferral of the title since Queen Elizabeth I knighted Sir Toby Belch". Egerton's wife, Lady (Moya) Egerton had her ALP membership restored in 1977, but Sir Jack was never reinstated to the party.
- Obituary, "Jumping Jack paid the price for the gong", Canberra Times, 29 December 1998, p. 13