Former foreign affairs minister John Baird is endorsing Christine Elliott in her bid to become the leader of the Ontario Progressive Conservatives.

Baird says Elliott "has the necessary leadership credentials" and the ability to put Ontario on the right track, saying he believes she is the only Tory candidate who can win the next provincial election in 2018.

The endorsement comes as Elliott is set to debate fellow leadership candidates Patrick Brown and Monte McNaughton in Ottawa tonight.

The race to replace former party leader Tim Hudak is down to just three candidates, after both Vic Fedeli and Lisa MacLeod bowed out last week and threw their support behind Elliott.

MacLeod says Baird's surprise decision to retire from politics was a key factor in her decision, though the Ottawa-area MPP says she hasn't yet decided if she will seek Baird's Ottawa West-Nepean federal seat once he officially resigns as an MP.

Brown, the Conservative MP for Barrie, Ont., is the only leadership hopeful who doesn't have a seat in the Ontario legislature.

Elliot — who was married to former finance minister Jim Flaherty, who died in April of last year — says Baird is the 23rd federal member of Parliament to support her bid for the party's leadership.