Trudeau is expected to make the announcement at a news conference in his Montreal riding of Papineau on Tuesday.
He's also expected to be speaking to the federal Liberal caucus at its regular weekly meeting this morning, but smiled and told reporters on his way in that he had nothing to announce.
Throughout the summer, Trudeau was non-committal when pressed about a potential run for the party's top job, citing his desire to spend more time with his children.
Two weeks ago, a leadership bid looked more plausible when rumours flared that Trudeau was ready to put his name in the ring.
A new Liberal leader will be chosen in April, after Michael Ignatieff resigned in the wake of the party’s disastrous showing in the last federal election.
Bob Rae, the interim Liberal leader, has already announced he won’t run.
Other leadership hopefuls
As for Trudeau's potential challengers, there's already talk that the party is putting pressure on Bank of Canada governor Mark Carney to run for the job.
Last April, Carney said in a television interview that he was not contemplating political life and was "absolutely focused" on his current job.
Toronto lawyer Deborah Coyne and Manitoba paramedic Shane Geschiere have announced they're interested in the leadership. Coyne is the mother of Justin Trudeau's half-sister, Sarah.
MPs Marc Garneau and Dominic LeBlanc are known to have leadership ambitions, but will have to evaluate their chances now that Trudeau is entering the ring.
Garneau was not commenting about his potential leadership bid Wednesday.
LeBlanc, who is the son of former governor general and Liberal cabinet minister Roméo LeBlanc, is expected to reveal his intentions later next week.
LeBlanc and Trudeau are longtime friends, dating back to their fathers' close relationship. On his way into caucus Wednesday morning, LeBlanc said Trudeau's candidacy would not affect their friendship.
Other Liberals said to be mulling over the decision to take the plunge include Ottawa MP David McGuinty, and former MPs Martin Cauchon, Gerard Kennedy, Mark Holland and Martha Hall Findlay, as well as former local candidates David Bertschi and Taleeb Noormohamed, and Toronto lawyer George Takach.
New rules and format for race
Veteran MPs expressed enthusiasm for Trudeau's bid Wednesday morning.
But Toronto MP Judy Sgro said it wasn't a foregone conclusion Trudeau will win.
"There are several very interesting people that are going to be running," Sgro said.
"He's a young man. He's got lots to learn just as you do and I do."
Another Montreal MP, former cabinet minister Denis Coderre, wouldn't rule out his own leadership ambitions, but said Trudeau adds a "dose of dynamism" to the race. He said he doesn't think Trudeau's candidacy will discourage other candidates from running.
"We need to have a real campaign this time, not a coronation," Coderre said.
"I think we're going to have a very strong number of serious people," said the Liberals' deputy leader Ralph Goodale.
Liberals announced the rules governing the leadership race earlier this month, including strict spending and debt limits.
Several candidates from the 2006 Liberal leadership race are still struggling to pay off their debts.
The next Liberal leader will not be chosen by delegates at a convention.
For the first time, not only card-carrying party members, but also a new category of party "supporters" will cast votes. The party hopes the change in format will inject new enthusiasm and strength into the party, now in third place in the House of Commons.Suggest a correction