Originally Thomas Harrison was an eleventh round draft pick of the Rangers' during the first complete Bantam OHL entry draft.  Thomas played his Bantam hockey up in Thunder Bay, near his hometown in northern Ontario.  Like most late round Bantam picks Harrison did not play for the Rangers in the season following his draft.  He returned to Thunder Bay, seen as a long shot at best how brought little more than size and some strength Harrison surprised almost everyone when he made the team as a rookie.  During his rookie season with the Rangers' also Peter DeBoer's first season coaching the Rangers, Harrison scored the only two goals of his career at this point.  Even during his rookie season Harrison found himself taking on some of the OHL's tougher heavyweights, which coincidentally included current Rangers' teammate: Nathan O'Nabigon.

Surprisingly O'Nabigon from Longlac also joined the Rangers and Thomas Harrison.  As he did during his first season, Harrison spent most of his second year with the Rangers playing on a line with T.J. Eason, a veteran defender on the Rangers' blueline during the Rangers' championship run in 2003.  Though in the postseason Harrison was only counted on for spot duty, he did shine when called upon during the third round of the playoffs when Marcus Smith went down injured and he saw a significant amount of ice time.  Harrison's knee let up late in 2002, but he elected to use a brace and continue playing into the postseason, with knee surgery in the offseason.

Harrison, traditionally a slow-starter would not be afforded a slow start during his third tour of duty with the Kitchener Rangers going into the 2003-'04 season.  Harrison was late in starting up after knee surgery, but in the words of head coach Peter DeBoer his dedication to conditioning and rehabilitation were an inspiration to the remainder of the team.  Apparently several teams inquired as to the availability of Harrison, but the Rangers in dire need of defensive help and veteran leadership as well as character after all of the grads from the previous season.

Thomas Harrison has become one of the top fighters in the entire OHL, now taking on all heavyweights.  In addition to that, Thomas is now on pace to have a career year offensively, and perhaps eclipse 10 points for the first time in his career, despite the fact that he started the season considerably late due to his injury.  In all three of Harrison's seasons in the OHL he has eclipsed the 100 penalty minute plateau.  During his third season with the Rangers, Harrison has played primarily with rookie's: Deveraux Heshmatpour and Matt Lashoff.