He said Cynthia Petersen, a Toronto-based lawyer who has argued several landmark Charter and gay rights cases before the Supreme Court of Canada, will probe allegations against two MPs he removed from the Liberal caucus.
Trudeau refused to speculate on the outcome of the investigation, how long it will take, or whether any part of Petersen's findings will be made public.
"I look forward to receiving her advice," Trudeau said Friday in St. John's. It was his first visit to the city since suspending Newfoundland MP Scott Andrews and Quebec MP Massimo Pacetti on Nov. 5, citing complaints of "serious personal misconduct."
Trudeau did not elaborate on the unproven allegations at the time. He refused again Friday to offer any details.
Trudeau said he hopes that the two unidentified female NDP MPs who have made the allegations will co-operate with Petersen. In any case, their allegations have been expressed to the party, he added.
Trudeau said he would like to see a proposed independent process involving the Speaker of the House of Commons progress.
Still, any recommendations from that investigation "will not be determining someone's eventual candidacy for the Liberal party or not, and that's why we've needed to set up a process as well."
Trudeau would not speculate when asked if he thought Petersen might report before the federal election next year.
Petersen declined to comment Friday.
Trudeau was in St. John's to speak to the city's board of trade Friday after promoting his close friend and local candidate Seamus O'Regan the night before.
The Liberal leader said he understands if constituents in the nearby Avalon riding, represented by Andrews since 2008, are frustrated by the lack of detail and the limbo in which they're left.
"They're not alone in considering this to be a distressing and difficult situation."
The allegations highlighted a glaring lack of any formal process to deal with harassment claims between MPs. A subcommittee of MPs from all three main parties was struck this week on Parliament Hill to develop such policies and procedures.
Andrews, a former ethics critic, has denied through a lawyer any wrongdoing since Trudeau suspended him. Pacetti has also denied the allegations.
Requests for comment to both men Friday were not immediately answered.
Sources familiar with the complaint against Andrews have told The Canadian Press in Ottawa that an unnamed NDP MP alleges he victimized her within the past six months.
The woman accusing Andrews has not spoken publicly and does not wish to file a formal complaint, according to the NDP.
The sources say the incident allegedly began at a social event on Parliament Hill before the woman, Andrews and Pacetti went from there to Pacetti's office, where they drank some wine. Pacetti eventually left, leaving Andrews and the woman alone.
The sources say the woman alleges Andrews followed her home, forced his way through her door, pushed her against a wall, groped her and ground his pelvis against her. The sources say she says she ordered him to leave and he did.
The woman further alleges that Andrews repeatedly called her a "c--kteaser" after the incident, according to the sources.
Andrews, a married father of two, has denied any misconduct and said he's confident a non-partisan process will find that no harassment occurred. But the sources say he has not given a detailed rebuttal to the woman's version of events that night.
His lawyer Chris MacLeod said last month in an email to The Canadian Press that Andrews was not provided with "any details of the internal summary or any documentation from the Liberal caucus" about the complaint against him.
"He is in no position to respond to an unknown allegation," it said.
Another unnamed NDP MP who has accused Pacetti of "sex without explicit consent" in March has said she would be willing to participate in a neutral, third-party investigation.
The Speaker of the House of Commons clarified in a letter to the NDP last week how that process might work but the party has not released the letter or said how the matter might move forward.
Pacetti has said in an email that he maintains his innocence and has refrained from speculation in the media since the allegations first surfaced.
"As with media reports of this nature, in this instance many questions remain unanswered and there is no way to evaluate the veracity of the claims being made," he has said in an email.
"I reaffirm my innocence and I will not comment on this matter in the media any further."
—with files from Jennifer Ditchburn in Ottawa.
Follow @suebailey on Twitter.