Hayden was born in Brisbane, Queensland. He attended Brisbane State High School and then joined the Queensland Police, working as a police officer for eight years while studying economics part-time at the University of Queensland. Hayden was elected to the House of Representatives at the 1961 federal election, aged 28 – along with Manfred Cross and Doug McClelland, Hayden is the earliest elected Labor MP still alive. When Gough Whitlam led the Labor Party to victory in 1972, he was made Minister for Social Security. He replaced Jim Cairns as Treasurer in 1975, but served for only five months before the government was dismissed.