O'Connor stood for the Senate at the 1901 federal election in March and was elected in the fourth position, with 40% of the vote (electors cast six votes, with the six candidates with the highest totals winning election). The only Protectionist Senator from New South Wales, he was appointed Leader of the Government in the Senate, and was instrumental in the evolution of that house as subordinate to the House of Representatives, although he encouraged the introduction of legislation into the Senate.
