He was born in Allegheny City (now in Pittsburgh), the older brother of Gertrude Stein.

Beginning in 1892, he studied at Harvard University in Cambridge, Massachusetts, for two years.

In 1897, he transferred to Johns Hopkins University in Baltimore, Maryland, where he graduated with a Bachelor of Arts degree in 1898.

In 1914, the two separated due to Leo's resentment of Gertrude's infatuation with Alice B. Toklas, whom he described as "a kind of abnormal vampire.

"[1] Stein returned to America to work as a journalist but eventually settled near Florence, Italy, with his long-time love interest, Nina Auzias.