He was a law clerk to Madam Justice Bertha Wilson of the Supreme Court of Canada in 1984-85.
Morgan teaches public international law, private international law, and international criminal law.
He started teaching in 1986, and from 1989-97 practiced at Davies, Ward & Beck in Toronto. Morgan has appeared at the Inter-American Court of Human Rights and the Decolonization Committee of the United Nations, and has provided expert evidence on international law to U.S. federal and state courts. He has testified on matters of law reform, national security, and foreign affairs before Parliamentary committees in the House of Commons and the Senate.
In July 2008, discussing a lawsuit for damages by the Palestinian village of Bil'in in Quebec Superior Court in Montreal against two companies registered in Montreal that are building and selling apartments in Modi'in Illit's new Matityahu East neighborhood, he said there while the move was "imaginative", there were obstacles in the case that might prevent it from prevailing. For one thing, The Geneva Convention was intended to apply to countries, and not to companies.
In December 2008, commenting on a House of Commons committee call for a review of the role and selection of the governor general, he noted that it would require amending Canada's Constitution. He said: "In Canada, the idea of tinkering with the Constitution is a tinderbox. It would have to be a really strong public sentiment to start the process for a constitutional amendment."
Commenting in September 2009 on efforts by Canadian tax officials to press UBS for details of Canadians who might be using UBS accounts to evade taxes, he said "They can go to court to try to compel UBS to disgorge names of Canadian taxpayers that have accounts there, but I'd say it's a toss-up as to whether they'd get that court order. It remains to be seen whether the courts think that banks are obliged to give up information about taxpayers that the taxpayers won't, on our voluntary disclosure system, give up."
When in February 2010 Toronto school Trustee Josh Matlow refused to apologize for criticizing a decision to spend $345,000 on a one-day conference, he said the board did not have a right to stop Matlow from speaking out, saying: "I think Matlow is doing exactly what we want school trustees to do. He's speaking his mind and speaking in criticism of board decisions. That's why we elect independent thinkers."