The 25-year old won the award after he ended his 2012 season in August to donate bone marrow to an anonymous leukaemia patient.
Seitz signed up to DKMS, the world’s largest bone-marrow center, in 2009 when he was playing with Real Salt Lake after teammate Andy William’s wife Marcia was diagnosed with a rare form of the blood disease.
He received a call earlier this year to donate to a perfect match and after discussions with those close to him, underwent surgery to have marrow removed from his pelvic bone, which kept him out of action for the remainder of the season.
Dallas head coach Schellas Hyndman, who is unsure if Seitz will be back with the club next season, was full of praise for the former Philadelphia Union gloveman’s efforts.
"It's not like we don't know him and haven't seen him," Hyndman told ESPN.com. "But his value as a person has gone off the charts.
“If it gets to a point where we are thinking, 'Do we bring back Chris, or do we not bring back Chris?' the one thing we will always say is his character and commitment is A-level."
Seitz won a weighted vote between MLS clubs, media and players from Sporting Kansas City’s Kei Kamara, Philly’s Michael Lahoud, New York Red Bull’s Kenny Cooper and Chivas USA’s Dan Kennedy.