The eighth season of Smallville, an American television series, began airing on September 18, 2008. The series recounts the early adventures of Kryptonian Clark Kent as he adjusts to life in the fictional town of Smallville, Kansas, during the years before he becomes Superman. The eighth season comprises 22 episodes and concluded its initial airing on May 14, 2009, marking the third season to air on The CW television network. Regular cast members during season eight include Tom Welling, Allison Mack, Erica Durance, Aaron Ashmore, along with new series regulars Cassidy Freeman, Sam Witwer, and Justin Hartley.

The Justice League is a fictional group of superheroes on the television series, Smallville, who were adapted for television by Alfred Gough and Miles Millar. The Justice League originally included Oliver Queen, Bart Allen, Victor Stone, and Arthur Curry; Clark Kent did not accept a role until three seasons later. As the team continued to appear in the series, new characters were introduced and subsequently joined the team. The original Justice League first appeared in the DC comic book The Brave and the Bold #28 (1960), and consisted of members Superman, Batman, Wonder Woman, Flash, Green Lantern, Aquaman, and the Martian Manhunter. In Smallville, the team did not make its first official appearance until the season six episode "Justice", although each member had been previously introduced individually on various episodes since season four. In the series, the team never formalized a name for themselves, although the cast and crew officially recognized the team as the "Justice League".