President of the Senate (Australia)
The position is provided for by Section 17 of the Constitution of Australia. The Senate elects one of its members as president at the start of each new term, or whenever the position is vacant. This is usually—though not necessarily—a member of the party or coalition that holds the most seats in the Senate. The largest party in the Senate is not always the governing party, as government is determined by the House of Representatives. The President of the Senate and the Speaker of the House of Representatives may consequently be from different parties.
2018 National Party of Australia leadership election
Under the Coalition agreement between the Liberal and National Parties, the Nationals' leader serves as deputy prime minister in a Coalition government. Therefore, the decision of National Party members would determine who succeeded Joyce as deputy PM. Following the 2016 election, sixteen National Party MPs sat in the Australian House of Representatives (including six from the Queensland Liberal National Party, and Joyce himself as a backbencher since his announcement). Some of the highest-profile National Party parliamentarians, namely deputy leader Bridget McKenzie and Resources Minister Matt Canavan, sit in the Senate; no senator has served as deputy prime minister in the history of the position.