Marshall Rothstein practiced law primarily in the fields of transportation and competition law and was a partner with the Winnipeg law firm of Aikins, MacAulay & Thorvaldson. From 1970 to 1992, he was a lecturer in transportation law at the University of Manitoba. In 1992, he was appointed to the Federal Court Trial Division, ex officio of the Court of Appeal, and appointed to the Court Martial Appeal Court of Canada. In 1999, he was appointed a Judge of the Federal Court of Canada, Appeal Division.