The 2005 Seattle Seahawks season was the franchise's 30th season in the National Football League (NFL), their fourth playing their home games at Qwest Field and their seventh season under head coach Mike Holmgren. They advanced to the National Football Conference (NFC) Championship Game, which was the first one for the franchise in 22 years, and they defeated the Carolina Panthers 34-14. In Super Bowl XL, they lost 21–10 to the Pittsburgh Steelers. The Seahawks compiled a 13–3 record in the regular season, easily winning the NFC West, a first-round bye, and home-field advantage in the NFC playoffs as the top seed for the first time in franchise history. There, they beat the Washington Redskins and Carolina Panthers to win the George Halas Trophy, and advance to their first ever Super Bowl. Combining the regular season and postseason, the Seahawks finished with a perfect 10–0 record at Qwest Field. The 2005 team was widely considered the best team in club history until the Super Bowl XLVIII championship. The 2005 season was also the team's 30th anniversary season in the NFL. The Seahawks were the only NFC team from the 2004 playoffs to qualify for the 2005 playoffs.

The Seahawks touted Pro Bowlers on offense, and boasted season MVP, running back Shaun Alexander, who would eventually break Priest Holmes's single-season touchdown record, with 28 total touchdowns. Alexander also led the league in rushing yards for the second consecutive year, which in turn helped the Seahawks lead the league in scoring. The offense was led by 7th-year veteran quarterback Matt Hasselbeck, who compiled a career-high and NFC leading 98.2 passer rating, while completing 65.5% of his passes, earning his second trip to the Pro Bowl. Future Hall of Famers Walter Jones and Steve Hutchinson anchored the offensive line at left tackle and guard respectively, and Mack Strong effectively blocked and rushed from the backfield at fullback on his way to a 2005 All-Pro Team selection. The team scored a franchise record 452 points, a record that stood until the 2020 team surpassed it with 459 points scored.

Although Seattle's strength was attributed to their offense, they were strong on the defensive side of the ball as well. The Seahawks compiled an NFL-leading 50 quarterback sacks, with defensive end Bryce Fisher leading the franchise with nine, while defensive tackle Rocky Bernard added 8.5 and veteran defensive end Grant Wistrom recorded four. Despite starting two rookies at linebacker for most of the year, the Seattle linebacking corps played well, led by Pro Bowler Lofa Tatupu, who topped the team with 104 tackles and added four sacks, three interceptions, and one fumble recovery. In the secondary, Michael Boulware led the team with four interceptions and also tallied two sacks and one fumble recovery, however Seattle suffered injuries throughout the year, notably to free safety Ken Hamlin. A bright spot in relief, second-year cornerback Jordan Babineaux played well as he appeared in all sixteen games for Seattle, intercepting three passes and making 61 tackles. For the season, the Seahawks defense ranked 7th in points allowed, surrendering just 271 total, 181 fewer than the Seahawks offense scored.

The period between the disappointing 2004 season and the start of the 2005 season was marked by major changes for the Seahawks, starting with the front office. Team owner Paul Allen fired eight-year incumbent General Manager Bob Whitsitt on January 14, the same day that Vice President of Football Operations Ted Thompson was hired away by the Green Bay Packers to be their general manager. Rumors had been floating that Whitsitt's relationship with coach Mike Holmgren (and almost everyone else) was strained and Holmgren later admitted that he had thought about leaving the team after a 2004 season that was personally draining. At the time of Whitsitt's firing the Seahawks salary cap situation was in extreme flux with 16 unsigned free agents on the roster including their three biggest stars Matt Hasselbeck, Shaun Alexander and Walter Jones. On February 3 Mike Reinfeldt, who had previously been pushed out of the Seahawks organization by Whitsitt, was hired back as a consultant to try to sort out the mess. Reinfeldt was able to sign Jones and Hasselbeck to long-term deals and put the Franchise Tag on Alexander, setting the stage for the rest of the off-season.

After a careful executive search the Seahawks settled on highly regarded personnel man Tim Ruskell as the new President of Football Operations on February 23, 2005. As a part of his roster overhaul, Ruskell subsequently released or neglected to re-sign six players (Anthony Simmons, Chad Brown, Orlando Huff, Chike Okeafor, Rashad Moore and Cedric Woodard) who were starters on an underperforming defense during the 2004 season. Over the rest of the offseason and into training camp Ruskell signed a raft of free agents to replace departed players on both sides of the ball, emphasizing character and work ethic in his evaluations.^{[citation needed]}

In the first round of the 2005 NFL draft the Seahawks traded down from pick 23 to pick 26 to select center Chris Spencer from the University of Mississippi and acquire an extra fourth-round pick. They then gave up two fourth-round picks to trade up into the second round and select USC linebacker Lofa Tatupu, who would start every game of the 2005 season and go to the Pro Bowl as a rookie.

at Superdome, New Orleans, Louisiana

at Qwest Field, Seattle