He was the second youngest of ten children born to Mary Ann (née Costello) and John Henry Kelly, an Irish immigrant.

Arthur Willis noted "Kelly appears to be anti-love, anti-romantic love, certainly, and distrustful of the tender emotions.

"[5] In his first full-length play, The Torch-Bearers, Kelly satirizes the "Little Theatre Movement", depicting it as made up of narcissistic and undisciplined amateurs.

In the first act, Kelly shows the troupe incapable of conducting a competent rehearsal; in the second, he depicts with farcical brilliance their public performance collapsing in shambles.

In his greatest popular and commercial success, The Show-Off, Kelly focuses his critique on the figure of Aubrey Piper, a loud, lying, self-deluded businessman with an obnoxious laugh and an obvious toupee.

Behold the Bridegroom (1927) shows a shallow and decadent flapper pine away when she meets a morally upright man who makes her realize her lack of character.

That Kelly was gay was a closely guarded secret and went unacknowledged by his family to the point of not inviting Weagley to his funeral; he instead slipped in and sat quietly on a back seat.