She joined the Legislation Section of the Department of Justice in 1970 and drafted such laws as the Access to Information Act, the Privacy Act, the Canada Health Act, the Official Languages Act, the Competition Act, the Customs Act and the Young Offenders Act. Dawson was made a Queen's Counsel in 1978. She was Associate Chief Legislative Counsel from 1980 to 1986 and Chair of the Statute Revision Commission through most of the 1980s. From 1986 to 1995, Mary Dawson was the head of the Department of Justice Public Law Sector, including the traditional public law areas of constitutional law, administrative law and international law as well as human rights law, native law, judicial affairs, access and privacy law and regulatory affairs. Dawson had a long career with the Government of Canada and oversaw a wide variety of legal issues from within the Department of Justice. She retired in 2005 as Associate Deputy Minister, a position she had held since 1988. Dawson played an important role in relation to constitutional matters. She was the final drafter for the patriation package and, until her retirement, drafted, and was the principal legal adviser for, all Constitutional amendments, including the Meech Lake Accord and the Charlottetown Accord. She led the legal team for the Government of Canada on the Quebec Secession Reference and was responsible for the legal advice on, and drafting of, the Clarity Act. Dawson also managed the Supreme Court Reference on same-sex marriage for the Government of Canada as well as the preparation of the related legislation. She advised extensively in the area of aboriginal rights. Dawson was a Skelton-Clark Fellow at Queen's University in 1999-2000 where she lectured in several faculties. She has also published several articles on various subjects. Dawson retired from the Department of Justice in 2005. After her retirement, Dawson acted as a consultant on a variety of projects, in both the public and private sectors. In June 2006, she was appointed to the Board of Governors of the Ottawa Hospital, and serves on a number of board committees. In 2014 Mary joined the Board of Help Lesotho. Dawson has also been involved in a number of international activities, as well as various outreach activities in Canada. She has held executive positions in the International Bar Association and was a Canadian member of the Joint Steering Committee of the Joint Canada-Russia project on Public Administration Reform in Russia. Dawson was named a Member of the Order of Canada in 2007.
