Senator Barnaby Joyce is the Nationals' choice to take on federal independent MP Tony Windsor for the NSW seat of New England.
Senator Joyce was the favourite to win the preselection race against 34-year-old software entrepreneur David Gregory.
NSW Nationals MP Niall Blair, who was chairing the preselection in Tamworth, said on Twitter that the ballot closed about 1pm (AEST).
Mr Blair then announced Senator Joyce as the victor.
Earlier on Saturday the senator told the ABC he was confident of a win at the party level but that his tilt against Mr Windsor, who holds his regional NSW seat with a margin of 21 per cent, would be a "momentous struggle".
Senator Joyce will now have to resign from the Senate by the time writs are issued for the September 14 election, and the Queensland Liberal Nationals will have to find a replacement for the Senate vacancy.