Romanowski played 243 consecutive games during the 1988-2003 seasons, an NFL record that stood until Chris Gardocki broke it during the 2006 season, finishing his career with 265, (256 reg. season and 9 playoff games). He won 4 Super Bowl Championships, and is the only linebacker to start 5 Super Bowls (Super Bowl XXIII, Super Bowl XXIV, Super Bowl XXXII, Super Bowl XXXIII and Super Bowl XXXVII). During his 16-year career, Romanowski compiled 1,105 tackles, 39.5 sacks, 18 forced fumbles, and 18 interceptions, which he returned for a net total of 98 yards and 1 career touchdown. Romanowski was a Pro Bowl selection twice, in 1996 and 1998, both during his tenure with the Denver Broncos.
Romanowski appeared in movies such as The Longest Yard, The Benchwarmers, Weiners, Bedtime Stories and Get Smart. Romanowski released an autobiography in 2005 titled Romo My Life on the Edge: Living Dreams and Slaying Dragons. The book became a New York Times best selling book in 2005. It chronicles his childhood, college, and his playing times in the NFL. He is also featured on the cover of the Midway Games title Blitz: The League and adds his voice as Bruno Battaglia, a linebacker in the game who wears his 53. He also appears in NCAA Football Series indirectly as LB #53 for the 1984 Boston College Eagles. In 2006, he founded Nutrition 53, a nutritional supplement company dedicated to optimal life performance. The company's name is derived from Romanowski's football jersey number, 53. Romanowski is active in the internet community and media through his personal blog, Facebook page and regular appearances on The Rick and Bubba Show and The Young Guns on WWZN in Boston.
In 2008, Romanowski was the defensive coordinator for the Piedmont High School (California) Highlanders Freshman Football team, where his son played.
In January 2009, Romanowski threw his name into the search for Mike Shanahan's replacement as the head coach of the Denver Broncos. Romanowski reportedly sent a 30-page PowerPoint presentation to team owner Pat Bowlen outlining his credentials and the new ideas he would bring to the team. The job was ultimately given to Josh McDaniels.
In February 2010, Romanowski was called in by Mike Shanahan to present to the Washington Redskins. Romanowski was inducted into the National Polish-American Sports Hall of Fame on June 23, 2011, in Troy, Michigan.
He is also a minority owner of NASCAR's Swan Racing in 2013. His own company Nutrition53 sponsored the team in 10 races in 2013.
Romanowski has been involved in numerous altercations with both teammates and opponents. In 1995, while with the Eagles, he was ejected from a game — and subsequently fined $4,500 — for kicking Arizona Cardinals fullback Larry Centers in the head.
Two more incidents occurred during the 1997 season while he played for the Broncos: In the first, he was fined $20,000 after a helmet-to-helmet hit on then-Carolina Panthers quarterback Kerry Collins in a preseason game resulting in Collins sustaining a broken jaw; in the second, Romanowski spat in the face of 49ers wide receiver J. J. Stokes in a regular-season game played in December on a Monday night in response to Stokes' taunting. Two years later, while still with the Broncos, he was fined a total of $42,500 for three illegal hits plus a punch thrown at Kansas City Chiefs tight end Tony Gonzalez, and was also fined an undisclosed amount for throwing a football at Bryan Cox of the New York Jets, the ball hitting him in the crotch area. In 2003, Romanowski attacked and injured one of his teammates, Marcus Williams, during a scrimmage. Williams, a backup tight end for the Oakland Raiders, was forced to retire after Romanowski confronted Williams after a play, ripped off his helmet, and crushed his eye socket with a punch. Williams sued for damages of $3.4 million, arguing that Romanowski had been suffering from "roid rage" when he attacked him. This argument was later rejected by the judge on the grounds that Williams could not prove that Romanowski had actually used steroids on the same day as the attack. Williams was awarded $340,000. Williams was quoted as saying he and his lawyers "just wanted to prove what was right and wrong about football".
He also had an appearance in the Spike television series Blue Mountain State. In the second-season premiere episode, Romanowski plays coach Marty Daniels' ex-brother-in-law and team consultant on dirty playing tactics.