On April 15 of 1942, Bithorn made history, when he pitched for the first time for the Chicago Cubs. Bithorn won nine games and lost fourteen his first year, but he rebounded to win 18 while losing twelve in 1943. That year, he led the league in shut-outs with seven, establishing a record for Puerto Rican pitchers that still stands.
Bithorn fought for the United States military in World War II, a fact which may have helped cut his baseball career short. In 1946, Bithorn was signed by the Pittsburgh Pirates, and in 1947, he saw two innings of action with the Chicago White Sox.
Bithorn went to Mexico in 1952, to attempt a comeback, through the Mexican baseball league, to the major leagues. In a confusing incident, he was shot to death on new year's eve, 1952.
Hiram Bithorn Stadium was opened in 1962. It is located next to Roberto Clemente Coliseum and across the street from Plaza las Americas, and it is one of the largest baseball facilities in Puerto Rico, and it also has hosted world championship boxing fights and important concerts.