Boston Red Sox was the last to integrate in 1959. The player that they signed was Pumpsie Green.
The last major league baseball team to sign an African-American player was the Boston Red Sox. The team passed on such great players as Willie Mays and Jackie Robinson.
Although they made half-hearted attempts to sign Black players in the 1960's, the team could not be said to be completely integrated until 1967, far later then any other team. The 1967 season was the first time in years that the Sox reached the World Series, but after that, a committment to integration faded until it was revived in the late 1970's.
It was the Boston Red Sox that was the last MLB team to integrate way back in the 1950s.