A professional from 2003 until 2011, he competed for the UFC, Bellator, Strikeforce, the XFC, and was a competitor on The Ultimate Fighter, fighting for Team Serra.
In the semifinal round, fighter Matt Arroyo suffered a rib injury and elected to pull out of the competition.
In a meeting to decide his replacement, Kolosci was the only fighter to express enthusiasm at the prospect of fighting Danzig and was granted the opportunity by UFC president Dana White.
At The Ultimate Fighter Finale, Kolosci lost to Matt Arroyo via armbar submission at 4:42 of the first round.
John and his girlfriend Cathy were married on November 20, 2009, in the ring during the intermission of the Hoosier Fight Club’s premier night.