After working as a speechwriter for federal Minister of Justice John Turner from 1968 until 1972,[3] Cotler entered academia in 1970 beginning his career as an associate professor at Osgoode Hall Law School.

[3] Cotler was a professor of law at McGill University and the director of its Human Rights Program from 1973 until his election as a Member of Parliament in 1999 for the Liberal Party of Canada.

[citation needed] He was tasked with improving relations with the indigenous peoples in Canada and implemented a policy "known as the seven R’s: recognition, respect, redress, representation, responsiveness, reconciliation and relationships.

This law, adopted in the wake of the September 11 attacks, had been criticized by some human rights groups and defense lawyers, as an unreasonable trade-off between security and freedom.

[12] On 22 February 2006, the Liberal Party appointed Cotler Critic for Public Safety and Emergency Preparedness in the opposition shadow cabinet for the 39th Canadian Parliament.

He was re-elected again in the 2011 election, fending off a serious challenge from former city councillor Saulie Zajdel, a longtime Liberal supporter running as a Conservative who lost by only 2,500 votes.

He said he would remain "active in public life, lecturing and writing on the issues of the day, advancing the causes of human rights and international justice, and advocating on behalf of political prisoners.

"[16] Cotler was one of thirteen Canadians banned from traveling to Russia under retaliatory sanctions imposed by Russian President Vladimir Putin in March 2014.

"[17] In November 2024, the Royal Canadian Mounted Police told Cotler that it had stopped an assassination attempt on him by the Iranian government the previous month.

The petition was signed by Elie Wiesel, Former UN High Commissioner for Human Rights Louise Arbour, and the former Swedish Deputy Prime Minister Per Ahlmark, and historian Yehuda Bauer.

[35][36] In 2012, Cotler advised Canadian foreign minister John Baird on rejecting the recognition of the State of Palestine during a United Nations meeting.

[37][38] In 2016, Irwin Cotler drafted the "'Never Again' Declaration", which has been signed by justice ministers, parliamentarians, jurists, and Luis Moreno Ocampo, former International Criminal Court prosecutor.

[45] However, in 1986, United Press International reported that Alan Dershowitz and Cotler were involved in an attempt to negotiate Mandela's release through a prisoner exchange.

[51] In 2017, Cotler was then asked to join a panel of independent international experts designated by Luis Almagro, the Secretary General of the Organization of American States, to determine whether there was reasonable ground to believe that crimes against humanity have been committed in Venezuela.

[52] Cotler's wife, Ariela (née Ze'evi), is a native of Jerusalem and worked as a legislative assistant to Likud members of the Israeli Knesset from 1967-79.

[3] Cotler became a step-father to Ariela's daughter Michal Cotler-Wunsh, who he adopted when the couple moved to Montreal, and the two had three other children; Gila, Tanya and Jonathan.