Despite a landslide win for the Ontario PCs on Thursday night, NDP Leader Jagmeet Singh said he's taking his party's showing as a portent of good things to come in next year's federal election.

"There's a promising sign in areas we've grown," he said in an appearance on CBC Radio's Metro Morning on Friday.

The NDP scooped up 40 seats in total in Ontario, securing their position as the Official Opposition and nearly doubling their wins in the 2014 election.

In addition to a sweep of Toronto's downtown core, the party made a major breakthrough in Brampton.

"We used to only hold one seat, my seat, and now we hold three seats, the majority of the ridings in Brampton," said Singh.

NDP leader Andrea Horwath held onto her seat in Hamilton Centre, where she has served as an MPP since 2004. (Frank Gunn/Canadian Press)

The Brampton wins are a family affair for Singh, with his brother, Gurratan Singh, winning the Brampton East contest by nearly 5,000 votes.

The NDP also blazed new territory in York South-Weston and Humber River-Black Creek, areas which both went Liberal in the last election.

"We've picked up seats in suburban ridings that we hadn't held. It shows that there's definitely an opportunity to grow," said Singh.

Still, Singh readily admits that the election result wasn't what he was hoping for.

"I'm really worried about what the Conservatives victory means to Ontario, the cuts that [Ford] is proposing, how deep and damaging they might be," he said.

"I'm confident that Andrea and the New Democrats will hold this government to account and be a fierce opposition."