In 1984, he was elected to the Western Australian Legislative Assembly as the member for Mount Lawley at a by-election resulting from the resignation from parliament of then premierRay O'Connor. Cash was re-elected in 1986 but the seat was abolished in a redistribution in 1988. He then switched to the Western Australian Legislative Council and was elected in the 1989 state election under the new proportional system which came into effect for the council. He served 20 years in that chamber, including four years as President between 1997 and 2001, while Richard Court was Premier, and was for several years thereafter the deputy president. He announced his retirement before the 2008 election, and his term ended on 21 May 2009.