When his father died, Booth won ALP pre-selection for his father's then-vacant seat of Kurri Kurri. At the resulting by-election on 8 October 1960, Booth was elected with 92.53% of the vote against a single Communist candidate. He was elected a further two times, in 1962 and 1965, but was elected uncontested as a candidate. He retained this seat until it was abolished in a redistribution prior to the 1968 election. Booth subsequently contested and won the recreated seat of Wallsend, gaining 75.83% of the vote. He would hold this seat through seven more elections in 1971, 1973, 1976, 1978, 1981, 1984 and 1988. Originally serving in the backbenches, with the election of Neville Wran as Leader of the party he was given the post of Shadow Minister for Education from 13 December 1973 to 14 May 1976. Following the Labor victory at the 1976 election, Booth, a prominent member of the Socialist Left faction of the New South Wales Labor, was sworn in as Minister of the Crown, serving as the Minister for Sport and Recreation and Minister for Tourism. He served on the Councils of the University of New South Wales from 1962 to 1965, Newcastle University College and its successor, Newcastle University from 1963 to 1974. As Minister for sports, he implemented a capital grants program and became popular among sporting organisations throughout NSW. On 13 August 1979, over a year after their 25th wedding anniversary, his wife Irene died from cancer, aged 47. On 29 February 1980 he was appointed Assistant Treasurer whilst retaining his other portfolios. Held these offices until 2 October 1981 when he was appointed as the Treasurer of New South Wales. As Treasurer, Booth introduced significant reforms, including program budgeting and reorganisation of the parliamentary public accounts committee, embodied in the Public Finance and Audit Act 1983 .
Later career
On 21 February 1982 Booth remarried to Gail Mathieson, an office executive, in Redfern. When his good friend and fellow left-faction member, Jack Ferguson, retired as Deputy Premier and Leader, Ferguson recommended Booth as his preferred successor, however, following some opposition from within the left faction, Booth lost the ballot to Ron Mulock. He remained as Treasurer until the defeat of the Unsworth Labor government at the state election in March 1988. In opposition Booth was appointed by the new Leader, Bob Carr, as Shadow Minister for Energy and Shadow Minister for Mineral Resources from 11 April 1988. He was accused by the new Minister for Administrative Services, Matt Singleton, of interfering, as Treasurer, with a Government office accommodation deal that resulted in $350,000 in dead rent. The unsubstantiated allegations infuriated the ALP Opposition and Booth was supported by Opposition Leader, Bob Carr. A subsequent Police inquiry cleared Booth of any wrongdoing. Booth however, did not live to see his name cleared and Carr commented that: "the tragedy of this case is that Ken Booth died before his name could be cleared". He died in office, survived by his daughter and his second wife, of a myocardial infarction on 1 November 1988 at his home and was cremated.
