The 2005 season was the Detroit Lions' 76th in the National Football League (NFL) and the third and final under head coach Steve Mariucci.

The Lions began their 2005 season with a 17–3 win over the rival Green Bay Packers.

However, the Lions lost five consecutive games following that win, and were eliminated from the playoffs with a 16–13 overtime loss to the Packers.

The season concluded with a 35–21 loss to the eventual Super Bowl XL champion Pittsburgh Steelers.

During the season, after the Lions lost 27–7 on Thanksgiving Day to the Atlanta Falcons, the Lions fired Steve Mariucci, and made defensive coordinator Dick Jauron to be the interim head coach for the remainder of the season.