Addington was born in Spartanburg, South Carolina. As a kid, he was a fan of dirt track races. At age 14, Addington's mother remarried and then the family moved to Batesville, Arkansas where his stepfather began working for Mark Martin. Although his stepfather worked for a successful Martin, Addington preferred to play football. He graduated from Central High School in Texas and moved back to Spartanburg. Addington's start in racing came as he helped friends compete in dirt cars.
Addington worked as Jason Keller's crew chief in the Busch Series, and the combination resulted in 10 wins, seven Top 10s, and finished in the season points. Addington worked in 2004 as the Joe Gibbs Racing crew chief for their #20 NASCAR Busch Series. Driver Mike Bliss finished fifth in points. In 2005, Addington was named the crew chief for Joe Gibbs Racing's #18 car driven by Bobby Labonte, replacing Mike "Fatback" McSwain. Labonte left for Petty Enterprises and was replaced by J. J. Yeley for two years. Kyle Busch replaced Yeley as the driver of the #18 car in 2008 and Addington remained as the crew chief. NASCAR observer's did not know what to expect from the combination, as the team did not just change its driver. It also changed from a Chevrolet car to a Toyota. On March 9, 2008, Addington scored his first win as a NASCAR Sprint Cup crew chief when the 18 team won the Kobalt Tools 500 in Atlanta, Georgia with driver Kyle Busch, and he was awarded the "Crew Chief of the Race". Busch lead the points with eight wins going into the Chase for the Cup. The team had numerous problems as soon as the Chase started, such as engine failures and wrecks, and Busch finished tenth in the twelve drivers in the Chase. Addington was named the DirecTV Crew Chief of the Year Award at NASCAR's award banquet. Busch ended the season with 21 victories in NASCAR's big three divisions, which was seven more wins that any driver had made since the Craftman Truck Series began in 1995. Busch said "I think the final ten races certainly humbled all of us. Everyone already had virtually guaranteed us the championship after seeing the first 26 races, but it changed so quickly." Addington was relieved of his crew chief duties with three races left in the 2009 season and Dave Rogers took over the role. On December 14, 2009, it was reported that Addington had accepted a deal to become the next crew chief for Kyle's brother Kurt Busch, replacing outgoing crew chief Pat Tryson, who had been relieved of his duties following the 2009 Sprint Cup Season. It is reported that the deal is for three years. Addington ended his tenure as Busch's crew chief at the end of 2011. He joined Stewart-Haas Racing owner/driver #14 Tony Stewart and Team Chevy, taking over for 2011 Sprint Cup Champion-winning crew chief Darian Grubb. Addington and Stewart had previous worked together at Joe Gibbs Racing. Addington was relieved of his duties as crew chief of the 14 on November 19, 2013. On November 21, 2013, it was announced that Addington would join HScott Motorsports in 2014 as a crew chief and competition director. On February 5, 2014, just days before the Daytona 500, it was confirmed that Addington would serve as the crew chief for the #51 team, whose driver would be Rookie of the Year candidate Justin Allgaier. In 2016, HScott Motorsports closed after the season ended, leaving Addington a free agent.
