The Biggest Loser: Second Chances is the eighth season of the NBC reality television series The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to Danny Cahill, the contestant with the highest percentage of weight lost. This season premiered on NBC on Tuesday, September 15, 2009.

The season's theme meant that each of the candidates had met with heartbreak and tragedy during their lifetime. Among notable stories, Shay Sorrells grew up in foster care while her mother unsuccessfully struggled with heroin addiction, while Abby Rike lost her husband and children in a head-on collision caused by a speeding driver. Amanda Arlauskas became a contestant after winning a public vote against Erinn Egbert held during the Season 7 live finale. Contestant Daniel Wright was a contestant in Season 7, and has returned to "finish what [he] started".

Another change to the format this year is that the two trainers will work with all contestants rather than splitting the contestants into two camps and creating an imagined competition between the two trainers. In the fifth week, when teams are changed to blue and black, Jillian leads black while Bob leads blue.