[2] From 1979 through 1981 Martineau worked as legal counsel for the President of the Canada Labour Relations Board, until he received a position as an associate at the firm Robert, Dansereau, Barré, Marchessault and Lauzon.
[2][3] In 1996, Martineau left Langlois Robert to create his own firm in Montreal that offered legal, arbitration, and mediation services.
[2][5] On June 27, 2007 Justice Martineau was appointed as a member of the Public Servants Disclosure Protection Tribunal, which was responsible for reviewing claims of reprisal from whistleblowers and taking appropriate actions based on the claims.
Three years later, Justice Martineau was appointed president of the tribunal.
On October 2, 2020 Justice Martineau was appointed to the position of Chairman of the Copyright Board of Canada, for a period of five years.