Maxwell is a Marquette University graduate with a BA in English, philosophy and political science. The founding Executive Director of American Rights at Work, she would be the first openly gay cabinet secretary if she were to be confirmed. Previous posts include National Field Director for Jobs with Justice and Deputy Field Director for NARAL Pro-Choice America. Maxwell also sits on the Board of Directors for American Families United and The Discount Foundation.

Maxwell is the second person endorsed by Human Rights Campaign for the post, along with California Congresswoman Linda Sánchez. "While we remain supportive of Representative Sánchez’s candidacy," said President Joe Solmonese, "it has come to our attention that Mary Beth Maxwell is also being considered for this crucial position. Given Ms. Maxwell's long history of leadership on labor issues, HRC is pleased to also endorse Mary Beth Maxwell for Secretary of Labor." Also backing her is former Congressman David Bonior.

Maxwell is an outspoken supporter of S.1041, known as the Employee Free Choice Act, which aims to bolster protections for unions and its represented employees as well as easing the process for workers to unionize if they choose to do so.