New Democratic Party Leader Dominic Cardy will run in the upcoming Rothesay byelection in the hope of winning the party's first seat in the legislature since 2005.

"The main reason is, as leader of the New Democrats, we have to show that we're ready to win seats across New Brunswick," he told CBC News.

Cardy officially announced Friday that he will seek the seat left empty by Progressive Conservative Margaret-Ann Blaney, who resigned as MLA earlier this month.

The byelection will be held on June 25.

The NDP will hold its nominating convention for the southwestern New Brunswick riding on Monday night.

The party does not currently have any seats in the legislature.

Cardy, who became leader of the NDP last year, disputes the idea that the relatively affluent riding is not a good fit for him.

"When you've got no seats, every seat seems kind of difficult. I don't view Rothesay as being any different. People have been talking like, 'Oh, there are all these well-off people.' New Democrats are winning seats across Canada in upper income communities, in lower income communities, because we have a message that's positive," he said.

Cardy doesn't think the riding is any more of a challenge than other constituencies.

"I don't think people in Rothesay necessarily have different views on issues like patronage and education and economic development from folks in other corners of the province," he said.

Tory stronghold

Cardy had previously joked with reporters that Rothesay is well-known as a "bastion for socialism" and would be a good fit for his left-leaning party.

Blaney, who stepped down to become the president and CEO of Efficiency New Brunswick, won a clear victory in 2010, earning 56 per cent of the vote, compared to 28.4 per cent for the Liberals and 8.9 per cent for the NDP.

In fact, the Tories have held the Rothesay riding, and its predecessor Saint John-Kings, since 1999.

But a recently-released NDP poll suggests the party is in first place in the Saint John area.

Interim Liberal Leader Victor Boudreau had challenged Cardy to run in Rothesay.

"He is the leader of the provincial New Democratic Party, he doesn't have a seat in the house, and this is an opportunity to show what he's made of," Boudreau had said.

The NDP has been without a seat in the legislature since Elizabeth Weir resigned to become president and chief executive officer of Efficiency New Brunswick in 2005.

The Tories will pick their candidate on Saturday, while the Liberals, who are currently in the middle of a leadership race, will hold their nominating convention on June 5.

The Progressive Conservatives currently have 41 seats in the legislature, the Liberals have 13.

Premier David Alward has said he feels good about the Tories' chances of winning the byelection.