Martinez played for Montreal from 1994 to 1997. He won the Cy Young Award as the National League's top pitcher in his final season with the Expos before being traded to Boston, where he won the American League version of the award twice.
Johnson made 11 appearances for the Expos at the start of his big-league career in 1988 and '89 before being traded to Seattle, where the 6-foot-10 "Big Unit" developed into one of the most feared pitchers in history.
Baseball writers elected four players for the first time since 1955, with Johnson, Martinez and Smoltz earning induction on the first try Tuesday. Biggio made it on the third attempt after falling two votes shy last year.
The quartet will be inducted in Cooperstown on July 26.
The Baseball Writers' Association of America had not given four players the necessary 75 per cent in a single year since selecting Joe DiMaggio, Gabby Hartnett, Ted Lyons and Dazzy Vance 60 years earlier.