In her youth, Maxwell was engaged in many Baháʼí activities.[5] At the age of 15, she joined the Executive Committee of the Fellowship of Canadian Youth for Peace.[5] She was also involved in local racial equality conventions, including dances.[6] A spectator, Sadie Oglesby – one of the first African-American Baháʼís [6] – described her as "sixteen-year-old Mary Maxwell, a beautiful and most refreshing girl to know".[6] By twenty-one, she was elected to the Local Spiritual Assembly of the Baháʼís of Montreal, the local Baháʼí governing council there.[5]