[2][3] In the 1941–1942 academic year, she took a leave from Columbia to be director of the Department of Social Work at the University of Puerto Rico.

[4] Cannon was one of the founders of the American Association of Hospital Social Workers,[5] and president of the organization in 1922–1923.

In 1949, Cannon was investigated by the House Committee on Un-American Activities, for her involvement in the Scientific and Cultural Conference for World Peace.

In 1950, Columbia University established the Mary Antoinette Cannon Fellowship, for social work students of Puerto Rican birth or parentage.

[10] Mary Antoinette Cannon shared a house in Greenwich Village from 1923 to 1962 with her partner Janet Thornton, a fellow Bryn Mawr alumna and a social worker based at the Columbia-Presbyterian Medical Center in New York City.