He made his Major League Baseball (MLB) debut with his hometown Brooklyn Dodgers at 16 years and 241 days old, starting at shortstop at Ebbets Field against the Chicago Cubs, on August 3, 1944, during the World War II manpower shortage.

Brown thus became the youngest non-pitcher to ever play in a major league game,[1] and the second-youngest overall after Joe Nuxhall, who was 15 years and 316 days old when he first appeared as a hurler for the Cincinnati Reds on June 10, 1944.

In Brown's debut game, he collected his first big-league hit, a double off the Cubs' Bob Chipman, and in the field handled three chances, with one error, as the Dodgers fell, 6–2.

[6] The next season, in a game against the Pittsburgh Pirates on August 20, 1945, Brown became the youngest player in MLB history to hit a home run, a record that still stands.

[11] Brown spent 1946 in the United States Army,[12] then in 1947, the second postwar season, returned to a Dodgers team with a set lineup that included Baseball Hall of Fame shortstop Pee Wee Reese.

[14] Brown's big-league career came to an end September 25, 1953, as a member of the Cubs; he had played in 494 games during all or parts of nine National League (NL) seasons, and was 25 years of age.