The Leader of the Opposition in South Australia is the leader of the largest minority political party or coalition of parties, known as the Opposition, in the House of Assembly of the Parliament of South Australia. By convention, the leader of the opposition is a member of the House of Assembly. The leader acts as the public face of the opposition, and acts as a chief critic of the government and ultimately attempt to portray the opposition as a feasible alternate government. They are also given certain additional rights under parliamentary standing orders, such as extended time limits for speeches. Should the opposition win an election, the Leader of the Opposition will be nominated to become the Premier of South Australia.

The Parliament of South Australia is the bicameral legislature of the Australian state of South Australia. It consists of the 47-seat House of Assembly and the 22-seat Legislative Council. General elections are held every 4 years, with all of the lower house and half of the upper house filled at each election. It follows a Westminster system of parliamentary government with the executive branch required to both sit in parliament and hold the confidence of the House of Assembly. The parliament is based at Parliament House on North Terrace in the state capital of Adelaide.