In a family that had a number of rowers grew up spawned, came Mary McCagg and her twin sister Elizabeth early with the rowing in touch.
McCagg and her sister attended Lakeside School, a private high school in Seattle. She then studied at Harvard University and was active in the local rowing team. Mary McCagg who studied child psychology, completed her degree in 1989 cum laude. After graduating she went to work for a children's book publisher. Today, she has worked for Candlewick Press in Cambridge.
From 1989 to 1997 she was a member of the U.S. National Rowing Team and won at this time eleven national championships, and various medals at World Rowing Championships and the Pan American Games. In the years 1992 and 1996 she participated at each of the Summer Olympic Games. After her playing career was McCagg member of the United States Olympic Committee and the United States Rowing Association. At the 2004 Summer Olympics, she was one of the U.S. delegation to an Assistant Chef de Mission.
Mary McCagg is married to the rower Kane Michael Larin since 1999.
In 2012 she and her sister from the National Rowing Foundation in the U.S. National Rowing Hall of Fame was recorded.