Gallner was born in West Chester, Pennsylvania. He started his career by following his sister along to one of her auditions.He proceeded to guest star on popular shows such as Judging Amy and Close to Home. Gallner joined the cast of Veronica Mars as Cassidy Casablancas toward the end of the show's first season, in May 2005 before becoming a season regular during the show's second season.After playing Bart Allen in the Smallville episode "Run", Gallner reprized his role on the January 18, 2007 episode "Justice" and the season 8 finale. He also guest starred on Cold Case as a teenage gunman, and recently appeared in the independent film Sublime. He guest starred in an episode of Law & Order: Special Victims Unit on October 9, 2007 titled "Impulsive" as a high school student who accuses his teacher (played by Melissa Joan Hart) of statutory rape.He also guest starred in an episode of Bones as Jeremy Farrell, the brother of a beauty pageant contestant and possible suspect of murdering one of the beauty pageants most renowned contestants.Gallner also played the lead role in an allegedly true-story-based horror film. The Haunting in Connecticut pits him playing a son with cancer, who becomes tormented by evil spirits. His family moves from New York to Connecticut to get him special treatment for the cancer, but the only house they can afford comes with a dodgy past. His character, Matt Campbell, is taken over by a dead spirit in the house and consequently sees a manner of disturbing sites. He cannot tell anyone because if he is reported hallucinating his treatment will be terminated. Although the Film over-all received little praise, Gallner was praised by many critics for his role, with one reviewer saying Gallner's acting was " very convincing".He was involved in the independent film "Cherry," filmed on the campuses of Kalamazoo College and Western Michigan University, along with several locations in downtown Kalamazoo, Michigan.He plays Aaron, an Ivy League freshman who meets and falls for an older woman while becoming the object of affection for her young daughter in the process.Kyle was cast as one of the lead roles, Quentin, in the reboot of A Nightmare on Elm Street. Quentin is the indie type guy that runs "Insomnia Radio" the school podcast. He is the boyfriend of Nancy. He was also cast in the indie film Unicorns written by Leah Meyerhoff. A story about an awkward teenage girl who escapes to a fantasy world when her first romantic relationship turns increasingly violent.