His father was Franklin James Kelley Sr (1858–1924) and his mother was Louise Ann Archer (1863–1952).

Flavin was married three times: to Daphne Virginia Springer on November 14, 1914, in Joliet, Illinois,[2] Sarah Keese Arnold in 1919, and Cornelia Clampett in 1949.

He and playwrights Perry Newberry, and Ira Remsen produced original dramas at the Carmel Arts and Crafts Club theater at that time.

[1] Flavin's play Broken Dishes (1929), which premiered on Broadway in 1930, served as the foundation for several screen adaptations.

He also owned a 1,300 acres (530 ha) ranch in the Cachagua area in upper Carmel Valley, California.