Marcus Cook Connelly was born on December 13, 1890, in McKeesport, Pennsylvania. His father, Patrick Joseph Connelly, was an actor and hotel owner, while his mother, Mabel Louise (maiden name Cook), was an actress.

From 1902 until 1907, Connelly attended Trinity Hall, a private school in Washington, Pennsylvania. From 1908 until 1915, he was a reporter and drama critic for several Pittsburgh newspapers. He then moved to New York, working as a newspaper journalist and freelance writer from 1916 until 1920.

Connelly became a prominent member of the "Vicious Circle" of the Algonquin Round Table, an informal group of sharp-witted writers, editors, actors, and intellectuals who met regularly at the Algonquin Hotel. In 1925, he was named to the editorial board of New Yorker magazine. In 1929, he wrote The Green Pastures, his most celebrated work, for which he won a Pulitzer Prize for Drama in 1930. In the same year, Collier's magazine published his short story...