Ross was born and raised in Bloomington, Indiana, the youngest of four children of Elsie Shockley Lockridge and the populist historian and lecturer Ross Lockridge Sr. Through his father, he was a double cousin of the future novelist Mary Jane Ward.
He graduated from Indiana University in 1935 with the highest average in the history of the university, despite having earned an unaccustomed B during two semesters at the Sorbonne in Paris.