Economist Erin Weir announced Wednesday that he is backing Saskatoon-based doctor Ryan Meili.
Weir said the two share many of the same ideas on resource revenues, climate change, retirement security and workers' rights.
"His book, his policy announcements during the campaign and his comments in leadership debates across the province reflect Ryan's commitment to many of the proposals that I have put forward. I believe that he is the candidate best positioned to ensure progressive leadership of our party," Weir said at a news conference in Regina.
The announcement comes two and a half weeks before New Democrats are to pick their new leader.
Weir said he made "an assessment" that Meili was ahead of him in the campaign and the timing was right to withdraw.
"This is certainly a very important juncture in the leadership race," said Weir.
"We finished a series of 14 debates all across the province and we still have a number of days left before the suggested deadline for party members to get their ballots in the mail, if they're voting that way."
Meili, standing next to Weir, would not speculate on what the move might mean for his chances on March 9.
"I'm always hesitant to comment on the horse race and say who's in first, who's in second," said Meili.
"All that I can say is this gives us one, a chance to connect to Erin's supporters and hopefully have them bring their support on board, but also to talk to those people who haven't made their decision — and there still is a large number of New Democrats who are undecided.
"This gives them, well, I suppose fewer choices, but also gives them some indication of some shared interest from two of the candidates and hopefully that will have some influence on their final decision."
Regina MLA Trent Wotherspoon and Saskatoon MLA Cam Broten are also vying for the leadership.
The winner will take over from John Nilson, who was been interim leader since Dwain Lingenfelter resigned after the 2011 provincial election.
Lingenfelter lost own his seat and the party dropped to nine seats in the 58-seat legislature.
Broten told radio station CJWW that just because Weir is supporting Meili, it doesn't mean his supporters will do the same.
"Ballots have been mailed out for some time, so a good amount of the membership has already voted," he said. "We just carry on, contacting our supporters and getting them out to vote, and try to convince those who are sitting on the fence.
"Erin brought a lot to the race but I don't think his exit will have a significant bearing on the outcome."
The new leader will face the task of rebuilding the NDP in Saskatchewan and challenging Brad Wall, a popular premier whose Saskatchewan Party won a record 64 per cent of the popular vote in the last election.
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