OTTAWA -- It was more Perry Mason than politics as usual, more cross-examination than question period -- and observers agree it was probably a key turning point in the electoral fortunes of Tom Mulcair and his New Democrats.

Instead of the usual House of Commons theatrics, the NDP leader, a former criminal lawyer, took a more prosecutorial approach in his efforts to trip up his hostile witness: Prime Minister Stephen Harper himself.

"On what date and at what time was the prime minister informed that Nigel Wright had made a payment to Conservative Sen. Mike Duffy?" he asked.

"If the leader of the NDP is suggesting that I had any information to the contrary from Mr. Wright prior to this, that is completely false," Harper retorted.

"Mr. Speaker, we are asking very simple, straightforward questions and the prime minister is not answering them," Mulcair shot back.

Tom Mulcair

Mulcair, 60, is no stranger to political theatre.

He has been flexing his political muscle for nearly three decades, but has remained largely an unknown quantity outside of Quebec -- something party brass have been keen to change during this campaign, particularly through advertising focused on his family life.

On the professional side, Mulcair worked as a lawyer, civil servant and eventually as a member of the National Assembly of Quebec in 1994, later serving as minister of sustainable development and environment and parks under Liberal Premier Jean Charest.

Monique Jerome-Forget, who served as Treasury Board president when Mulcair was environment minister, remembers him as a "very supportive, solid soldier in the team."

"He's certainly a strong person. It's not negative for a prime minister," said Jerome-Forget. "You don't want somebody who bends over backwards to accommodate a thousand people all at once."

Former leader Jack Layton eventually wooed Mulcair into the federal fold, where he became the sole NDP MP from the province in 2007, elected in the riding of Outremont.

In 2011, the New Democrats were able to achieve historic electoral success, forming the official Opposition for the first time, thanks to remarkable gains in Mulcair's home province, where the party claimed 59 of 75 available seats.

Layton died just 113 days later, touching off a difficult leadership race, Mulcair writes in his newly released autobiography, "Strength of Conviction."

"Undergoing such a contest at such a painful time -- with the media and other parties posing as judge and jury -- was an especially unwelcome burden."

Tom Mulcair at Layton memorial

During the course of the 2012 contest, former leader Ed Broadbent came out against Mulcair, warning he would take the party towards the centre of the political spectrum.

Broadbent, who backed former party president Brian Topp in his leadership bid, said his relationship with Mulcair has evolved a great deal since then.

"Three years ago is a long time ago in politics," he said. "It was a matter of getting to know him and watching him. I wouldn't want to ignore the evidence of exceptional performance. "

The NDP, which is calling for the Senate to be abolished, has also capitalized on other upper chamber controversies that popped up in the wake of the Duffy affair.

Party insiders also say Mulcair has worked diligently behind the scenes to ensure his team, made up many first-time MPs, doesn't make rookie mistakes.

"Many critics were suggesting that without Jack, that the caucus would not be cohesive, would not be as effective," said NDP senior campaign adviser Brad Lavigne, a longtime confidant to Layton.

"It was clearly under Tom Mulcair's leadership that the caucus was governed with discipline and hard work."

Former NDP deputy leader Libby Davies says Mulcair's leadership has been an anchor for the party.

"He is a very on-the-ground guy," she said. "He's very good at assessing what is going on out there and communicating that back to his caucus in a realistic way."

"Boy, if there's anyone to take on Stephen Harper, it is Thomas Mulcair."

Mulcair's greatest challenge will be to translate his political strengths into more seats for the New Democrats.

Recent public opinion polls have suggested support for the party has slipped during the 11-week campaign.

But Mulcair insists he isn't concerned.

"Whatever the polls have shown, I've said the same thing," Mulcair said in Halifax this week. "For the first time in Canadian history, we have a three-way race."