Former New Democrat MP Olivia Chow hopes to return to national politics, running in the federal election to be held almost exactly a year after she lost her bid to be mayor of Canada's biggest city.

"I refuse to stand on the sideline while we can deliver change," Chow said Tuesday, pointing to the NDP's plan to provide one million affordable daycare spaces across the country.

Chow suggested she's returning to politics in part because it's possible the NDP could move from Official Opposition to government.

In an interview to air on CBC News Network's Power & Politics at 5 p.m. ET, Chow pointed to the chance of NDP success in the coming federal election.

"We are on an edge of forming a government that could deliver finally high-quality and affordable child care. It's so exciting and that's why I want to contribute my experience and make it happen," she told host Rosemary Barton.

Chow will run for the NDP in the same general downtown Toronto area she represented for years, although her former riding now has a new name and different boundaries.

Chow, the widow of onetime NDP leader Jack Layton, resigned her seat in Parliament in 2014 to run in Toronto's mayoral election, which she lost to John Tory. Now, she'll face off with Vaughan, a former city councillor who captured the Trinity–Spadina riding for the Liberal Party last summer.

Former New Democrat MP Olivia Chow said Tuesday she'll run for the NDP in Spadina—Fort York, a riding that encompasses most of downtown Toronto. (CBC)

That riding, which Chow represented for eight years, was redistributed and renamed Spadina—Fort York in the redrawing of Canada's electoral boundaries last year that will see the addition of 30 ridings in this election.

Spadina—Fort York encompasses much of the downtown core as well as the city's waterfront, a space that's seen a tremendous condo boom.

Tough race against Vaughan

Despite her popularity, she's likely to face a tough race against Vaughan, a former journalist, who is also popular in the downtown riding.

Chow emphasized that she had already represented many parts of the riding, as well as her work in Toronto on affordable child care. Asked about how she would take on Vaughan, Chow spoke of past Liberal Party promises to provide a national daycare program.

Liberal MP Adam Vaughan, left, will face a challenge by New Democrat Olivia Chow in Toronto's Spadina—Fort York riding. (Aaron Vincent Elkaim/Canadian Press)

"Nothing personal against Adam Vaughan. It's the Liberal Party that disappoints," she said.

"I remember the disappointment I felt in '93 at the Red Book promise for a national child-care program. I remember '97, disappointed again. And then there was 2000. It was over and over again. After 13 years of Liberal government, they just didn't get it done."

But Vaughan took a slightly sharper approach. In a video posted to Vaughan's website Monday, he said he isn't taking the job "just because [he wants] a job in politics." He doesn't refer to Chow directly.

"It takes more than just wanting to be a politician. You have to make politics work for people," Vaughan said in the video.

At a press conference Tuesday afternoon, Vaughan said the NDP's child-care plan won't be up and running for five or six years, and will need $3-billion in provincial funding. He also argued it won't create new spaces.

"It's a great slogan ... the real issue is can you deliver," Vaughan said.

Stop 'making political calculations'

The NDP defeated the Liberals over the 2005 federal budget, he said, which contained a national child-care agreement (Chow got her seat in Parliament in the subsequent election).

"The NDP voted to defeat that budget, roll the dice and they gave us 10 years of Stephen Harper," Vaughan said. "It's time we stopped making political calculations and looking for political opportunities, and instead start delivering the services Canadians need."

Chow, also a former Toronto councillor and school trustee, is currently serving as a distinguished visiting professor with Ryerson University's Faculty of Arts, where her work focuses on community engagement and democratic participation. Chow said she'll take a leave of absence from Ryerson.

Layton's children, Sarah and Mike Layton, appeared with Chow and Mulcair at Tuesday's press conference.

In the 2014 mayoral election, Chow won 226,879 votes — or 23 per cent of the overall vote — to finish third behind Tory and Doug Ford, the brother of former mayor Rob Ford.

In the 2011 federal race, Chow won the previous riding by more than 20,000 votes. Vaughan won the byelection to replace Chow with 6,745 votes. He beat the NDP's Joe Cressy, who has worked closely with Chow in the past.

The Conservative candidate in Spadina—Fort York is Sabrina Zuniga. The Green Party doesn't have a candidate listed for the riding.

(See a related graphic about the riding from The Canadian Press.)