Born in Bronxville, New York, Mary is the youngest American athlete to represent America at the World Championships.
The American middle distance athlete ran for Bronxville High School winning 2 national titles. In 2010 she was Champion in NYS Class C & NYS federation. Two years later she won the World Junior title breaking the American high school girl’s outdoor record in the 1500m with a 4:11.01.
Cain set a new record in the University of Washington Indoor meet in the 3000 meters running a time of 9:02.10, an accomplishment which saw USA Track & Field name her as Athlete of the Week.
Another high school record tumbled, also in January of 2013, when she recorded a time of 4:32.78 for the indoor mile in New York City.
By February she had broken the indoor record for the 2 mile at the Boston Indoor Games running 9:38.68.
Once more youth, junior and high school records fell in June at here first IAAF Diamond League event… she became the first American youth to break the 2 minute barrier in the 800m with a time of 1:59.51.
At the 2013 USA Outdoor Track and Field Championships, Cain qualified for the World Championships at the age of just 17 in the 1500m with a second place time of 4:28.76.
She once again made history competing in the final at such a young age and in November of the same year it was announced she would turn professional and run for the Nike Oregon Project.
On December 3, 2013 she was named Youth Athlete of the Year by USATF.