A brilliant scholar, it was said that he would communicate on the field in Latin with a fellow linguist. After graduating college magna cum laude in 1923, he was drafted to play shortstop for the Brooklyn Dodgers, where by most accounts he began a rather mediocre professional baseball career. Of Berg, one teammate quipped "He can speak seven languages, but he can't hit in any of them."
Standing 6-foot-1, 185-pounds, Berg played a total of 15 major league seasons, where he was a lifetime .243 hitter. Although he started out as a utility infielder throughout the majority of his career he primarily played as a catcher and mostly as a backup player. He also played for the Chicago White Sox, Cleveland Indians, Washington Senators and Boston Red Sox. In 1939 he retired from baseball after a knee injury had forced him to play for some time as a reserve player.
While an average (for a major leaguer) ballplayer, Berg's real strength was in his intellect and daring. In fact, during his baseball career he managed to graduate from Columbia Law School second in his class, and study at the Sorbonne in Paris, despite the rigors of his schedule.
In 1934, Berg participated in a tour of Japan with an all star team that included the likes of Babe Ruth and Lou Gehrig. It was here that it is believed he started his career as a spy. Before the trip Berg had been recruited as a spy for the United States. It is said that after he gave a speech (in Japanese) as a lecturer at Meiji University, Berg climbed to the rooftop of a Tokyo hospital where he proceeded to remove a camera concealed by his kimono and take photographs of the skyline, harbor and industrial sections of the city. Apparently during World War II, U.S. pilots used these very photographs for bombing raids of Tokyo.
In 1943, after Berg had completely retired from baseball and had begun working full time for the United States government as a goodwill ambassador to Latin America, he became an officer in the OSS (Office of Strategic Services) the forerunner of the CIA.
Some of his assignments included: Planning a plot to assassinate Werner Heisenberg, the head of Nazi Germany's atom-bomb project, which was aborted after coming to the conclusion that Germany was not close to building this kind of bomb; being parachuted into Yugoslavia and meeting up with the partisan Tito; traveling throughout Germany in 1944 and 1945 helping arrange the capture of prominent German atomic scientists by the U.S., before the Soviets could get to him; and traveling throughout Czechoslovakia as a spy with fellow agents.
In the late 1940s Berg was forced out of the spy business. Never married, he spent the rest of his life living with various relatives as what could be called a freeloader. In fact, his brother Sam once was forced to send him two eviction notices to get him to leave his house.
Some biographers and historians conjecture that Berg's baseball career was merely a cover for his spying activities, however, Berg always maintained that he truly loved baseball and that his career as a spy began in earnest.
Berg planned to write an autobiography detailing his career as a spy but died in 1972 of an abdominal aortic aneurysm, never having written the book.