Margaret Mary Marvin, 59, who returned to college after rearing five children received a degree last spring, died of a brain tumor Monday at her home in Potomac.

Mrs. Marvin had attended the College of St. Catherine in St. Paul, Minn., and the University of Minnesota but left school in 1942 to marry Robert S. Marvin. Three years ago, she entered a liberal arts program at Georgetown University, completed her remaining courses, and was granted a bachelor of arts degree by the College of St. Catherine. She returned there to receive her diploma at graduation exercises in May.

She was born in Sioux Falls, S.D., and grew up in Minneapolis and St. Paul. She had been a resident of Montgomery County since 1949 and of Potomac for the past 25 years.

Mrs. Marvin was a founding member of Our Lady of Mercy Catholic Church in Potomac. She had served as perfect of its Sodality and chairman of the parish library. She also was a member of the original Archdiocesan Planning Committee for Adult Education. As a perish coordinator for refugee relief, she had organized the activities for helping a Cambodian family sponsored by the parish.

In addition to her husband, of Potomac, she is survived by two daughters, Kathleen M. Abrams of Silver Spring, and Patricia M. of Roanoke, Va.; three sons, Robert S. II of Charlottesville, Va., and John F. and David W., both of Amherst, Mass.; her mother, Ruth McGuire of St. Paul; two brothers, William W. McGuire Jr. of Glenview, III, and John J. McGuire of St. Paul, and six grandchildren.