Tyron Whitten has claimed Western Australia's final spot in the upper house for the party, after the Australian Electoral Commission finalised results in the state on Thursday.
Queensland One Nation senator Malcolm Roberts has also been re-elected in the Sunshine State following a close race for the final position.
The Senate results mean One Nation will increase from two to three seats in the upper house, its highest representation in Canberra since 2016.
The pair of senators will join Senator Hanson, who still has another three years left on her term, in the next parliament.
The final results in WA confirmed two senators from Labor, Ellie Whiteaker and Varun Ghosh, while Slade Brockman and Mattt O'Sullivan will represent the Liberals, with Green Jordon Steele-John also being re-elected.
Labor will increase its numbers in the Senate from Queensland, claiming two slots - Nita Green and Corinne Mulholland - while the coalition will also have two positions - Paul Scarr and Susan McDonald.
Newly elected Greens leader Larissa Waters was also confirmed to have won another six years in the upper house, taking the fifth slot in the state.
The final lot of Senate results will be announced on Friday morning, which will include the final seat in NSW that's yet to be decided.
With all but one of the Senate spots declared, Labor holds 28 of the 76 seats in the chamber, with the coalition on 27, the Greens on 11, One Nation with three and six being on the crossbench.
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