Knaus was born in Rockford, Illinois, and grew up around short-track racing, helping his father John compete at Rockford Speedway against the likes of Mark Martin, Alan Kulwicki, Rusty Wallace, and Dick Trickle. By the age of 14, Knaus was already serving as crew chief during his father's Rockford Speedway championship season. The father-and-son team also won the Great Northern Series championship and finished second in the NASCAR Winston Racing Series. Knaus graduated from Jefferson High School in 1989 and moved to North Carolina in 1991 to pursue a career in national-level stock car racing.
After working briefly with Stanley Smith's stock car team, Knaus joined Hendrick Motorsports and was assigned to the No. 24 car driven by Jeff Gordon. From 1993 to 1997, he progressed from general fabricator to overseeing the entire chassis and body construction program. He was a member of Gordon's "Rainbow Warriors" pit crew, serving as a rear tire changer, and was part of the 1995 and 1997 championship teams.
Following the 1997 season, Knaus moved to Dale Earnhardt Incorporated as car chief, working with the No. 1 team driven by Steve Park and later Darrell Waltrip. He subsequently joined Tyler Jet Motorsports before moving to Melling Racing in 1999 at the invitation of Ray Evernham, who was building Dodge's Cup Series program. At Melling, Knaus was promoted to crew chief for driver Stacy Compton in October 2000.
Knaus returned to Hendrick Motorsports for the 2002 season, assigned as crew chief to rookie driver Jimmie Johnson in the No. 48 car. The partnership immediately showed promise: the team recorded three race wins in Johnson's debut year and would go on to rewrite NASCAR's record books.
The duo won their first Cup Series championship in 2006. Consecutive championships in 2007 and 2008 tied Cale Yarborough's record of three straight titles. A fourth championship in 2009 was unprecedented in the modern era, and a fifth straight in 2010 produced a record that stood as one of the most dominant sustained runs in American motorsport. After Johnson failed to win a sixth consecutive title in 2011, Knaus and Johnson rebounded to win a sixth championship in 2013 and a seventh in 2016, equaling the career totals of NASCAR's all-time great drivers.
Among the notable episodes in the partnership was the 2016 season finale at Homestead-Miami Speedway, where Johnson started at the rear of the field due to an unapproved body modification penalty. He drove through the field, took the lead in the closing laps, and won both the race and the championship — his seventh.
Knaus also led the No. 48 to wins at marquee events including multiple Daytona 500s (though he was suspended when Johnson won the 2006 edition) and multiple Coca-Cola 600 victories.
Knaus's tenure was marked by periodic confrontations with NASCAR's technical inspectors. In March 2001, he received a two-race suspension — the first safety violation penalty issued in the wake of Dale Earnhardt's death — for a seatbelt infraction at Atlanta Motor Speedway. His most significant suspension came in 2007, when he was fined $100,000 and suspended for six races over the shape of fenders on the No. 48 car at the Toyota/Save Mart 350 at Infineon Raceway. In 2012, he was again suspended six races and fined $100,000 after the No. 48 car failed pre-race inspection for the Daytona 500, though the suspension was later rescinded on appeal while the financial penalty stood.
In October 2018, Hendrick Motorsports announced that Knaus would be reassigned from the No. 48 to the No. 24 car of William Byron for the 2019 season, ending his sixteen-year run with Johnson. Byron scored his first career win in 2020 with Knaus on the pit box. In September 2020, Knaus stepped down from the pit box and assumed the role of Vice President of Competition at Hendrick Motorsports, a position focused on overseeing the technical and competitive direction of the organization.
Knaus was inducted into the NASCAR Hall of Fame on January 19, 2024. He is widely considered one of the greatest crew chiefs in the sport's history, recognized for his strategic acuity, attention to technical detail, and his ability to execute consistently in high-pressure championship scenarios.