Ewell was born in Owensboro, Kentucky, the son of Martine (née Yewell) and Samuel William Tompkins. His family expected him to follow in their footsteps as lawyers or whiskey and tobacco dealers, but Ewell decided to pursue acting instead. He began acting in summer stock in 1928 with Don Ameche before moving to New York City in 1931. He enrolled in the Actors Studio.
