Selinger captured all 117 delegates during a party meeting in Winnipeg's Maples constituency on the weekend, giving him 258 so far.
He used the social media site Twitter on Monday to send a note saying the win was a "great birthday present."
Former cabinet minister Theresa Oswald, who did not compete in The Maples, is second with 208 delegates.
Steve Ashton, the third contender, has 177 but stresses there's still a long way to go before the leadership election on March 8 at a convention in Winnipeg.
He's expected to grab most of the northern constituencies, which carry a large number of delegates who will use mail-in ballots to vote.
Oswald has announced that Michael Balagus, a longtime NDP strategist and chief of staff for former premier Gary Doer, will help run her 2016 election campaign if she wins.
Balagus ran the NDP campaign in 2011 when Selinger was re-elected with a record number of seats in the legislature. (CJOB)
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