Trudeau is speaking to reporters at 12:30 p.m. ET following his party's weekly caucus meeting, and Cotler is expected to join him. CBCnews.ca will carrying the press scrum live.
The 73-year old Liberal human rights and international justice critic was first elected in 1999 and was Attorney General and the minister of justice in the governments of Jean Chrétien and Paul Martin.
In a statement released by the Liberal Party, Cotler is quoted saying he intends to stay in his seat until the election, expected in 2015, and then will continue "the pursuit of justice in other arenas."
Cotler also said in the statement, "I am particularly proud of my time as minister, during which I introduced Canada’s first law to combat human trafficking, crafted the Civil Marriage Act – landmark legislation that extended marriage equality to gays and lesbians while at the same time guaranteeing religious freedom."
Cotler, who represents the historic Montreal riding of Mount Royal, recently attended Nelson Mandela's memorial service in South Africa because, as an international human rights lawyer, he had served as one of Mandela's counsels while he was in prison.
With Cotler's move, Trudeau is losing the kind of experience and institutional knowledge in the Liberal front bench that he also faced when the former Liberal interim leader, Bob Rae, retired from politics in the summer.
There was speculation over Cotler's future this week when it was reported that Anthony Housefather, the mayor of Côte Saint-Luc, Que., was interested in the Liberal nomination in Cotler's riding.
It's not the first time Cotler dealt with speculation about his future.
In the fall of 2011, six months after the last general election, a series of robocalls from the Conservative Party were directed at people in Cotler's riding suggesting he might soon retire and asking for support if there were to be a byelection.
When Cotler complained in the House of Commons about the misleading calls, Speaker Andrew Scheer described the calls as "reprehensible."
Cotler, a lawyer and law professor at Montreal's McGill University, has received 10 honorary doctorates and is an officer of the Order of Canada.