Jay enjoyed his entire minor hockey experience playing in his hometown of Whitby, Ontario. After his graduation from the Whitby Minor Hockey Association (WMHA), he played one season for the Oshawa Legionnaires of the Ontario Junior Hockey League (OJHL), winning the BJ Monroe Trophy as the league’s Top Pro Prospect and the Jack Ferguson award, commonly known as the “Fergie”, as the player selected first overall in the 1998 Ontario Hockey League (OHL) Priority Selection.
Jay was selected first overall in that draft by the Brampton Battalion, giving him the added distinction of being the first-ever pick in the history of the franchise. Harrison played his entire 4-year OHL career with the Battalion, and was selected to represent Canada at the IIHF World Junior Hockey Championships on two occasions. He was a medalist in each tournament, earning a bronze medal in 2001 and silver in 2002.
Harrison was selected in the third round of the 2001 National Hockey League (NHL) Entry Draft, 82nd overall, by the Toronto Maple Leafs, and he made his NHL debut in 2006 against the Montreal Canadiens. In 2007, Jay signed a 1-year contract with EV Zug of the National League A in Switzerland. Honing his skills and gaining valuable experience overseas, Jay returned to North America in early 2008 to rejoin the Maple Leafs for the remainder of that season.
In the summer of 2008, Jay signed with the Carolina Hurricanes of the NHL where he established himself as an everyday defenseman over six-plus seasons. The pinnacle of his career came in 2013, when he represented Canada at the IIHF World Hockey Championships in Stockholm, Sweden.
In 2014, Jay was traded to the Winnipeg Jets where he played the final two years of his professional career. He played in 372 games over the course of his NHL career, registering 23 goals, 52 assists, and 360 penalty minutes.