Shortly before her death at the age of 39, New York theatre critic Joseph N. Ireland wrote of Gannon, "[she] is now universally acknowledged to be the best general comic actress in the city.
"[2] Born in New York City on October 8, 1829, Gannon was the daughter of Irish immigrants and began her career as a child actress sometime between 1832 and 1835.
[2] She made her debut in Philadelphia on January 18, 1838, at the Walnut Street Theatre, as Lady Flennap, in Garrick's farce of Lilliput.
In 1841 she played an engagement at the American (afterwards Barnum's) Museum, appearing in six characters and executing a dance from La Bayadere in the vaudeville of The Actress of All Work.
[3] She had a series of critical triumphs at the Wallack's Theatre where she performed as a leading comedic actress beginning in 1855 up until her death thirteen years later.