The Leader of the Opposition in the Senate is a party office held by the Opposition's most senior member of the Shadow Cabinet in the Australian Senate, elected to lead the opposition party in the body. Though the leader in the Senate does not have the power of the office of Leader of the Opposition, there are some parallels between the latter's status in the lower house and the former's in the Senate. In addition to his or her own shadow ministerial portfolio, the leader has overarching responsibility for all policy areas and acts as the opposition's principal spokesperson in the upper house. The leader is entitled to sit at the table of the Senate, and has priority in gaining recognition from the President of the Senate to speak in debate. Another similarity is that the leader typically announces changes to opposition officeholders in the Senate, including shadow ministers, party leadership and whips. The leader also has some responsibility for appointing opposition senators to committees, a role filled by the Manager of Opposition Business and whips in the lower house. The current leader is Simon Birmingham. He is assisted by a Deputy Leader of the Opposition in the Senate, currently Michaelia Cash.

The Senate is the upper house of the bicameral Parliament of Australia, the lower house being the House of Representatives. The composition and powers of the Senate are established in Chapter I of the Constitution of Australia. There are a total of 76 senators: 12 are elected from each of the six Australian states regardless of population and 2 from each of the two self-governing internal Australian territories. Senators are popularly elected under the single transferable vote system of proportional representation.