In a scene that could well become a routine sight in the House of Commons, Trudeau found himself in the traditional leader's role, beginning the Liberal line of queries during question period.
The front-running leadership hopeful read his three questions — on the government's reported plan to take back control over manpower training from the provinces — from a sheet of paper.
"It is time the members opposite learned that they were elected by Canadians to represent their views here in Ottawa, not the prime minister's views in their communities," Trudeau intoned amid heckling from the Conservative benches.
Despite his uninspired, stilted delivery, Trudeau won a standing ovation from Liberal MPs, most of whom are backing his leadership bid.
But if the normally unscripted Trudeau didn't seem at ease, neither did the prime minister.
Harper stumbled in response to Trudeau's questions, twice referring to him as the "minister" for Papineau, before finally getting in a weak riposte.
"I welcome the member for Papineau in showing up and making the views of his constituents known for a change in the House of Commons."
Trudeau has rarely been in the Commons since launching his leadership campaign in early October. He's been almost constantly on the road, giving passionate stem-winders to adoring crowds across the country — in stark contrast to Thursday's performance in the Commons.
However, even before the leadership contest, he wasn't known as a stellar or frequent performer in the Commons.
Probably his most famous contribution to parliamentary debate came just over a year ago when he used a profanity to describe Environment Minister Peter Kent, an epithet for which he quickly apologized.
Trudeau candidly acknowledged last spring that Commons theatre is not his strong suit, when he was asked about rumours he might be willing to serve as interim leader during the campaign for a new permanent leader.
"I'd make a terrible interim leader," Trudeau said then. "My strengths are outside of the House, not inside the House."
Parliamentary veteran Bob Rae ultimately chose to stay on as interim leader and has been widely applauded for doing a masterful job of holding down the Liberal fort during the leadership contest.
While Trudeau is clearly no Rae, it's some consolation to him that neither are Marc Garneau or Joyce Murray — the only other leadership hopefuls who currently hold seats in the Commons.
Both Murray and Garneau were given chances last fall to lead off for the Liberals during question period.
Neither particularly shone and neither elicited a response from Harper, who normally responds only to questions from the NDP and Liberal leaders, leaving his ministers to parry all other opposition queries.