Thomas was the first Virgin Islander to play in the major leagues; his mother gave birth to Thomas in Santurce, Puerto Rico, because of better medical care available there, returning to their native Saint Croix immediately after his birth.

Thomas was listed as 5 feet 9 inches (1.75 m) tall and 165 pounds (75 kg); he threw and batted right-handed.

His professional career began in 1951; then, after a three-year hiatus, it resumed in 1955 in the Class C Provincial League in the Canadian province of Quebec.

In his five-year major league career (1957–61), he played for five different home cities: the New York / San Francisco Giants (1957–1958), Philadelphia Phillies (1959), Baltimore Orioles (1960) and Cleveland Indians (1961).

Thomas was one of the original San Francisco Giants, opening the 1958 season as their starting catcher in their first-ever official game on the West Coast.