Manitoba NDP officials say membership has more than doubled since Gary Doer announced his resignation in August.
The deadline to sign up new party members ahead of the upcoming Manitoba NDP leadership convention on Oct. 17 ended Thursday.
New memberships are still being processed, but party officials said they expect the number of members to have risen to more than 11,000 from about 5,000 when the count is done.
Starting Sunday, meetings will be held in individual constituencies to select the party delegates who will vote to determine the next leader and premier.
MLAs Steve Ashton, Andrew Swan and Greg Selinger are all vying for the position.
Doer, the provincial NDP leader since 1988 and the premier of Manitoba since 1999, surprised many political observers by announcing Aug. 27 that he was stepping down, ending his reign as the longest-serving of Canada's current premiers.
The following day, he was introduced in Ottawa by Prime Minister Stephen Harper as Canada's next ambassador to the United States.
Doer has not set a date for his final day at the party helm.