Buckley appeared in the 1998 thriller science fiction film, Disturbing Behavior, alongside Actress Katie Holmes. In 2001 he starred in an indie film Extreme Days a comedy-drama-romance flick. In 2005, Buckley was offered the part of Adam Ross on the hit crime drama CSI: NY. The part was supposed to be a recurring role, but by the end of the show's third season in 2007 he was offered a five-year contract. Before receiving the role of Adam Ross, Buckley had appeared as a different character on the original CSI: Crime Scene Investigation in a 2004 episode.

In 2006, the film Jimmy and Judy was released, the first fully interactive 3D cyber world. When the CSI: NY episode featuring Buckley aired in 2006, Director Randall K. Rubin called Buckley to discuss the success of an episode of CSI: NY, entitled "Down the Rabbit Hole" and the internet activity it had generated for Buckley. Harold Whaley, program Director for Urban Network, suggested the idea of an in-world premiere featuring Buckley as a guest host and panelist for a post screening Q&A.

Buckley proposed to his girlfriend of two years, Abigail Ochse on December 31, 2012 while on vacation in Hawaii. On September 3, 2013 Buckley announced they were expecting a baby girl. The couple welcomed daughter Willow Phoenix Buckley on January 19, 2014. On October 24, 2014 while in New Zealand, Buckley fractured his arm and leg while running away during a "scare event".