A graduate of DePauw University, Marillyn Zacharis earned her master's degree at Indiana University and taught high school English for five years in California, Indiana, and Pennsylvania. In 1972, she moved to Massachusetts with her late husband, John Zacharis, who had joined the Emerson College faculty and later became its president. She was elected to the Emerson Board of Trustees in 1996 and currently serves as its secretary. As chair of the board's development committee, she led a campaign to raise funds to build an 11-story performance and development center, and provided the leadership gift for the campaign. The center, named in memory of Zacharis's parents, Norman I. and Mary Tufte, opened in 2003.
Zacharis is also an honorary trustee of the Worcester County Horticultural Society, which operates Tower Hill Botanical Garden. She served as manager of the Masterworks Chorale in Boston for 18 years and was its board president after retiring from the manager position. She is an active supporter of the Ploughshares literary journal at Emerson and an overseer at the Boston Symphony Orchestra. She currently cochairs the funding campaign for ArtsEmerson with a leading gift, sings with an a cappella group, and teaches part time at Regis College. She has served on the Conservation Commission as well as the Finance Committee for the Town of Weston, where she resides, and as the town's representative to the Metropolitan Area Planning Council (MAPC). She has also been active in the League of Women Voters of Massachusetts (president, 1989–1991) and WGBH-TV.