Ackles was born in Dallas, Texas, the son of Donna Joan (née Shaffer) and Alan Roger Ackles, an actor. He has a brother, Josh, and a sister, Mackenzie. Ackles had planned to study sports medicine at Texas Tech University and to become a physical therapist but instead moved to Los Angeles to start his acting career.
After modeling on and off since the age of 4, Ackles began to concentrate on an acting career in 1996. He appeared in several guest roles on Mr. Rhodes, Sweet Valley High, and Cybill before joining the cast of the NBC soap opera Days of Our Lives as Eric Brady in 1997. He won a 1998 Soap Opera Digest Award for Best Male Newcomer and went on to be nominated three times (in 1998, 1999, and 2000) for a Daytime Emmy Award for Outstanding Younger Actor in a Drama Series for his work on Days of our Lives.
Ackles departed Days of our Lives in 2000 and went on to appear in the mini-series Blonde, about the life of Marilyn Monroe. He also auditioned for the role of the young Clark Kent on Smallville, a role offered to actor Tom Welling instead. Next he appeared in a guest role on the James Cameron television series Dark Angel on Fox in 2001 as serial killer Ben/X5-493, the brother of main characterMax/X5-452 (played by Jessica Alba). His character died in the episode, but Ackles returned to the show as a series regular in the second season as Ben's sane clone, Alec/X5-494. He remained with the show until its cancellation in 2002.
Ackles worked steadily throughout 2003. He joined the cast of the WB's hit show Dawson's Creek during its final season, playing CJ, Jen Lindley's lover. Afterward, Ackles filmed several episodes of the unaired series Still Life for Fox before it was abruptly dropped. He also had a small role in the 2004 short filmThe Plight of Clownana. Ackles was the producer's first choice to play Eliza Dushku's love interest on the second season of Tru Calling, Ackles turned down the role, which was then offered to Eric Christian Olsen and the character's name was changed to "Jensen" because the producers of Tru Calling liked Ackles' name. Ackles returned to Vancouver (where Dark Angel was filmed) in 2004 to become a regular on Smallville playing the assistant football coach Jason Teague, who was also the newest romantic interest for Lana Lang (played by Kristin Kreuk). He also had a lead role in the 2005 film Devour in which Ackles' father, actor Alan Ackles, also had a role playing the father of Ackles' character, Jake Gray.
Finally, Ackles joined the cast of the CW horror/drama series Supernatural in 2005, where he stars as Dean Winchester. Dean and his brother Sam (Jared Padalecki) drive throughout the United States hunting paranormal predators, sometimes with their father, John (Jeffrey Dean Morgan). The show is currently in its eleventh season.
Ackles plays Dean Winchester a fictional character and one of the two protagonists of the American drama television series Supernatural.