The Toronto ridings of Trinity-Spadina and Scarborough-Agincourt have each chosen Liberal candidates to represent them in Ottawa in byelections held Monday.

Former Toronto city councillor and Liberal party darling Adam Vaughan took the closely-watched downtown Trinity-Spadina riding, while former lawyer Arnold Chan won in Scarborough-Agincourt.

Vaughan stepped down from his job as a Toronto councillor in order to take a run at a federal seat. The former journalist won the Liberal nomination in the riding last month. His election in Trinity-Spadina is a significant victory for the Liberals, as the NDP's Olivia Chow had held the riding since 2006.

"The residents of Trinity Spadina have given me an extraordinary honour and I'm profoundly grateful," said Vaughan to a crowd of lively supporters gathered at the Steamwhistle brewery for a post-election party and speech.

Vaughan also reached out to who he called "new Liberals."

"You don't win elections, you don't build parties and you don't change governments without bringing new people into the conversation," he said to cheers.

Within 90 minutes of the polls closing, Joe Cressy, the New Democrat candidate in Trinity-Spadina, tweeted that he had phoned to congratulate Vaughan on his victory.

"I honestly thought we had it. Adam is a formidable challenger. He's served in this community for a while. Residents decided he had earned it and I had more to prove," Cressy told the crowd of supporters gathered at his post-election party.

Vaughan bested Cressy by some 20 percentage points.

Preview of 2015?

NDP Leader Tom Mulcair spoke at Cressy's event, telling the crowd that the ridings the Liberals won Monday will "change in the next campaign."

"The work that you've done now is in the bank for the next time around," he said.

The results could be a portent of things to come in 2015. Trinity-Spadina has always been something of a bellwether: when the Liberals have won the riding in the past, they've won power nationally; when the NDP has won the riding, the Conservatives have taken power.

In a clear indication of the riding's national political importance, Vaughan was joined by Liberal Leader Justin Trudeau during his victory speech Monday night.

"The results of these byelections have proven that our message is reaching and engaging Canadians," Liberal Leader Justin Trudeau said.

The vacancy in Trinity-Spadina was created when Chow stepped down as the MP for the riding, so that she could pursue a mayoral bid in Toronto. The riding saw multiple visits from both NDP Leader Tom Mulcair and Trudeau during the byelection campaign.

Liberals hold Scarborough

Chan, who managed to increase the Liberal's share of the vote in Scarborough-Agincourt to about 60 per cent, is a lawyer and former political aide at the Ontario legislature. His win means that the riding, which was represented for 25 years by Liberal Jim Karygiannis, will remain in the party's hands.

The Conservatives, who saw the potential for an upset in the riding when Karygiannis stepped aside, tried to appeal to the conservative values of the ethnically diverse suburban population with attacks on Trudeau's support for legalization of marijuana.

Chan called his victory a repudiation of the Conservative party's "negative attacks" on Trudeau, accusing it of trying to suppress votes by scheduling the byelections for the day before Canada Day, when many voters were taking an extended weekend.

Thanking his supporters and his fellow candidates on Monday night, Chan said that he believed the decisive victory was powered by the hard work of his team.

The 49-year-old Scarborough-Agincourt MP posted on his website Wednesday that he intends to maintain a modified work schedule while undergoing cancer treatment and is confident he can beat the disease. (Chantal Da Silva-CBC/Radio Canada)

Early estimates of voter turnout were low, with about 29 per cent of eligible voters casting a ballot, but the riding saw the highest turnout of the four up for grabs in Monday's byelections.

Karygiannis announced in the spring that he, too, was stepping down to pursue an opportunity at the municipal level. He's since registered to run for city council this fall in Ward 39, which is also known as Scarborough-Agincourt.

June has been a busy month for voters living in these two Toronto ridings. In addition to Monday's byelections, residents also voted in the provincial election less than three weeks ago.

The twin byelections in Toronto were just two of four taking place on the day before Canada Day. The other two were in Alberta, in the ridings of Fort McMurray-Athabasca and Macleod.

In those byelections, Conservative candidates John Barlow and David Yurdiga won in Macleod and Fort McMurray-Athabasca, as was expected.