Marzano, who played for the Red Sox, Rangers and Mariners, was in his second season as an on-air personality at MLB.com.
"John was a beloved member of our team, a personable, terrific friend to all with whom he worked," said Bob Bowman, CEO of MLB Advanced Media. "He was an engaging, informed interviewer. His energy, knowledge of the game and comedic touch produced admirable results. We miss him dearly already."
MLB.com will immediately establish an internship program in memory of Marzano, who in addition to being drafted 14th overall in 1984 earned a spot on Team USA for the Olympics.
"Words cannot describe how sorry we are to have lost John's inspiring presence, but rest assured, his spirit and legacy will always influence us," said Dinn Mann, MLB.com's EVP of Content. "Our prayers go out to his family, his friends and his fans. John simply gave his all every time he went about doing his job and living his life, always grateful, always striving."
A native of South Philadelphia and born on Valentine's Day in 1963, Marzano, a member of the Temple University Hall of Fame, showed tremendous work ethic and determination as a ballplayer and broadcaster.
Marzano played 10 seasons as a catcher in the Majors. The Red Sox weren't the first team to draft him. The Twins picked him in the third round in 1981 out of high school, but Marzano elected to go to college. Marzano reached the big leagues within three years after starring at Temple, playing for Boston from 1987-1992. He was in the Cleveland and Philadelphia farm systems for two years, then, in 1995, appeared in two games for the Texas Rangers. In 1996, he earned a spot on Lou Piniella's Seattle roster and spent three years with the Mariners.
After retiring as a player, Marzano worked for WIP radio in Philadelphia and at Comcast SportsNet as a post-game analyst for Phillies games before catching on full time with MLB.com in 2007.
Marzano was co-host with Vinny Micucci of "Leading Off" on MLB.com"s Baseball Channel every weekday at 9 a.m. Marzano impressed those around him until the day he died, regularly delivering instructive insight and humor in his role.
"(Ken Griffey Jr.) lifts and separates better than any hitter I have ever seen," Marzano said during a recent show, breaking down a highlight. "Having an opportunity to watch this man play for three years, I was so fortunate -- even though I was sitting on the bench watching him. To watch him and the plays he made in center field, crashing into walls, sometimes getting hurt, not worrying about himself but worrying about his team, it was amazing for me to watch that."
Marzano is survived by his wife Terri, daughters Dominique and Danielle, and two grandchildren.