Barnaby Joyce has been elected unopposed as leader of the Nationals, with Senator Fiona Nash chosen as deputy among a field of seven candidates.

LISTEN ABOVE: Australian correspondent Murray Olds speaks to Mike Hosking

Mr Joyce, who replaces retiring leader Warren Truss, last night declared his elevation, which means he will also be deputy prime minister, in what he says will be an "awesome responsibility".

Mr Joyce told reporters after the vote that the party's responsibility was to "country people and people in towns ... people in the brick and tile, those on the farm, those on the coast", while also paying tribute to outgoing leader Warren Truss.

He becomes the 13th leader of the party, while Senator Nash, the first woman to be put in a leadership position in the Nationals, will also move into the cabinet, joining five other Liberal female MPs.

Mr Truss said earlier the coalition agreement will retain its basic points, but will have to be renegotiated between Mr Joyce and Mr Turnbull.