Mabelle H. Cowan's grandparents were Irish immigrants. The daughter of hatmaker Gilbert Cowan, she lost her mother early she attended Saint Vincent Academy, a Catholic college/preparatory high school sponsored by the Sisters of Charity of Saint Elizabeth.

In the 1910 Census she lists herself as 'Music Teacher - Private Family'.

In the 1920s there are many newspaper references to her performing on various New Jersey-based radio stations, the earliest being December 1922 where she accompanied a soprano and violiniste. A 1923 listing mentions a radio broadcast by three 13-year-old pupils of 'Miss Mabelle Cowan of Orange', and the most interesting is a broadcast of 'Mabelle Cowan's Orchestra' on 20th March 1925.

Her first Atlas rolls appear around 1927, and like most of that companies' releases, are outstandingly creative and jazzy performances.

In the 1930 Census she was still unmarried at age 43, living at home with her brother, sister, and elderly father. She lists her profession as 'school music teacher'.

She died, still unmarried, in 1970 aged 84.