Gillies was the second overall pick by the Saskatoon Blades in the 2004 Western Hockey LeagueBantam Draft. Gillies spent parts of four seasons with the Blades, but the team struggled and consequently Gillies played in only 10 playoff games during his major junior career. Still, he gained attention with his strong physical and two-way play, and was selected to represent Canada at the 2007 IIHF World U18 Championships in Finland, where Canada finished 4th overall. . That summer he was selected in the first round of the NHL draft by the Minnesota Wild, who traded up three spots in the draft in order to pick Gillies 16th overall. Gillies was named captain of the Blades during the 2007-08 season and again represented his country at the 2008 World Junior Championships in the Czech Republic where he helped Canada to its fourth consecutive gold medal at the tournament. Late in the 2007-08 season Gillies made his professional debut with the Wild's American Hockey League affiliate, the Houston Aeros. He managed 8 points in 11 games with the team. That fall he cracked the Wild roster out of training camp and went on to play 45 games for the team during the 2008-09 season. Gillies recorded his first career point, an assist, on October 11, 2008 against the Boston Bruins, and his first career goal on December 19, 2008 against the New York Islanders. Gillies spent the entirety of the 2009-10 season developing his game with the Aeros. Though he would remain with the Aeros for the majority of the 2010-11 season, Gillies was re-called by the Wild on April 3, 2011. He played the final 7 games of the season with Minnesota, contributing a goal in the last game of the season, a 5-3 victory over the Dallas Stars that ended the Stars' bid for the final playoff spot in the Western Conference. On July 6, 2011, Gillies signed a two-year contract extension with the Wild. In the 2011–12 season, Gillies struggled to establish a role with the Wild, assisting on only 2 goals in 37 games before on January 13, 2012, he was placed on waivers. The following day he was claimed by the Columbus Blue Jackets. A free agent approaching the 2013-14 season, Gillies accepted an invite to attend the Buffalo Sabres training camp. Unable to secure a contract with the Sabres he was reassigned to their AHL affiliate, the Rochester Americans training camp, on September 21, 2013. He was then signed to a one-year AHL deal with the Americans on September 25, 2013. As a free agent again in the off-season, Gillies participated in his second consecutive training camp on a try-out with the New York Islanders. Gillies was assigned to AHL affiliate, the Bridgeport Sound Tigers on a professional try-out to begin the 2014–15 season, before signing a one-year AHL deal on December 12, 2014.
