Hendin joined the St. Louis Cardinals in 1973 as assistant public relations director. In 1995, he was named vice president of community relations in which he became responsible for representing the Cardinals at various events in the St. Louis-area and on many civic and charitable boards and committees. He also was responsible for special events such as opening day, anniversary activities and coordinating on-field, pre-game activities. A native St. Louisan, Marty was a graduate of University City High School and the University of Missouri-St. Louis. He was selected Ad Man of the Year in 1987 by the Advertising Club of Greater St. Louis and was named Good Guy by the St. Louis Chapter of the Baseball Writers Association in 2006.