Overshadowed by her sister Betty, the sisters both sang as members of the Vincent Lopez Orchestra starting in 1938. Marion was discovered by Glenn Miller when he heard the sisters perform in Boston. In September of the same year, she was invited to join the Glenn Miller Orchestra.
Well-liked in the group, Marion seemed to exude a "girl-next-door" type of personality, and Miller briefly changed her name to Sissy Jones, allegedly to reflect this. In the summer of 1939, Marion was replaced temporarily by Kay Starr, when she collapsed from exhaustion. She returned shortly afterwards, but was discovered by a gossip columnist to be pregnant in early 1941. Although she was married and, at the time, still able to perform for several more months, she resigned out of embarrassment, and was replaced by Dorothy Claire.
Marion returned to the group in August, and performed until the group's final night, 27 September 1942, crying through the night. After the group disbanded, she continued singing and had a small acting career.
In the 1960s, she married Vic Shoen, music director for the Andrews Sisters. They moved to Kirkland, Washington, where Marion was the director of Residence XII, a women's alcoholic treatment centre, and died on 10 January 1987.