the Kadina Town Council in 1971. He served as mayor from 1974 to 1977, reputedly "South Australia's youngest ever mayor". He was the final mayor before the town was merged into the District Council of Kadina. In 1976, Olsen was elected president of the Liberal Party of Australia (South Australian Division), serving until 1979. He was first elected to the South Australian House of Assembly at the 1979 election as a Liberal in the Barossa Valley seat of Rocky River. He represented this seat, renamed Custance at the 1985 election, until 1990. Olsen's political career was marked by a bitter rivalry with Dean Brown, the two representing the conservative and moderate wings of the South Australian Liberal Party respectively. After the 1982 election and the electoral defeat and retirement of David Tonkin, Olsen defeated Brown for the state Liberal Party leadership and became Leader of the Opposition. Up against the Labor premier John Bannon, Olsen lost both the 1985 election and 1989 election. In the latter election, the Liberals won a majority of the two-party vote (52 percent) with a five-seat swing. However, most of that majority was wasted on landslides in the Liberals' rural heartland. Even with the likely support of the one National Party MP, the Liberals were still one seat short of making Olsen Premier. Olsen resigned as state Liberal leader soon after the election and returned to the backbench. He was appointed to the Australian Senate in 1990 to fill a casual vacancy caused by the resignation of Tony Messner. However, in 1992, after less than two years in the Senate, he resigned to return to state politics. The Bannon government was under pressure from the collapse of the State Bank of South Australia. However, Olsen's successor as state Liberal leader, Dale Baker, was unable to gain significant ground. Baker resigned as state Liberal leader in 1992 and called a spill for all leadership positions, intending to hand the leadership back to Olsen as soon as he was securely back in the legislature. To facilitate this, former Deputy Premier Roger Goldsworthy, a leading member of the Liberals' right wing, resigned his seat of Kavel, based on Mount Barker, and handed it to Olsen. However, several members of the party's moderate wing were unwilling to see Olsen take the leadership uncontested. They arranged for leading party moderate Ted Chapman to give up his seat of Alexandra and