Dominic Cardy announced Friday he will seek his party's nomination as a candidate in the riding of Rothesay, where a byelection is set for June 25.
The seat became vacant when former Conservative energy minister Margaret-Ann Blaney announced last month that she was quitting politics.
Blaney has been appointed president of Efficiency NB, a provincial Crown corporation that promotes energy efficiency.
The New Democrats received less than 10 per cent of the vote in Rothesay during the most recent provincial election, but Cardy said he's confident he'll improve on that.
"I'm in this to win," he said Friday. "I think the people in Rothesay, just like the folks across the rest of the province, are ready for a change."
"I think the way the government has behaved with the appointment of Margaret-Ann Blaney, the issues around patronage and the whole lack of direction the province is facing, by putting a leader in the house who would stand up for the interests of the people in the province would be appealing to the folks there."
The governing Conservatives currently hold 41 seats in the legislature, while the Liberals hold 13.
The New Democrats have not held a seat in the legislature since 2005 when Elizabeth Weir quit her Saint John seat to become president of Efficiency New Brunswick.