Ousted Corangamite MP Sarah Henderson has won a bruising internal battle between warring factions to claim a highly sought vacant Senate seat.

Four months after she was voted out of the government's most marginal seat in a knife-edge campaign, Ms Henderson was on Sunday endorsed by the Liberal Party to replace former communications minister Mitch Fifield.

Senator-elect Sarah Henderson thanked the Prime Minister and Treasurer for their support. Credit:Scott McNaughton

Mr Fifield resigned from Parliament to take up an appointment as Australia's next ambassador to the United Nations.

The contest between Ms Henderson and Greg Mirabella was considered too close to call in the days before the vote, with internal Liberal Party sources reluctant to predict a winner.