Marilyn Trenholme Counsell OC ONB (born October 22, 1933) is a Canadian lecturer, doctor and politician.
She was born in Baie Verte, New Brunswick, the daughter of Harry Frederick and Mildred (née Baxter) Trenholme.
She was appointed to the Senate in 2003 by Governor General Adrienne Clarkson, on the advice of Prime Minister Jean Chrétien, and sat as a member of the Liberal caucus.
In 2008, she began lecturing on Political Leadership in Canada at Mount Allison University.
She received honorary degrees from l'universite de Moncton, Mount Allison and University of New Brunswick and was also honoured with the Sir Charles Tupper Award for Political Action (CMA) and the Champion of Public Education Award (TLP).