Mulcair and Borlase will hold a public meeting at the United Steelworkers office in Labrador City Tuesday night.
Borlase was elected by the party on Sunday night, winning the candidacy to run against former MP Peter Penashue, who resigned amidst talks of spending irregularities in his 2011 election campaign.
The NDP selected a candidate despite calls from the Green Party of Canada to stand down in the byelection on the grounds that a concerted opposition could prevent a Conservative from winning.
The federal Conservatives announced early on that Penashue would run as their candidate in the byelection.
Liberals have not announced a candidate or a date for a decision. However, Liberal MHA for Cartwright-L'Anse au Clair Yvonne Jones announced that she would be stepping down from her role as MHA to run as a candidate.
Todd Russell, the former Liberal MP for Labrador, made the decision not to seek the candidacy and focus on his duties as the president of NunatuKavut.