Coughlin began his NHRA career in the Sportsman divisions, claiming his first world championship in 1992 by winning the NHRA Super Gas category. Over the years he also accumulated 12 wins in the NHRA Lucas Oil Sportsman Series across various classes. He is one of only two professional drag racers to have won a national event in seven different classes: Pro Stock, Competition, Super Stock, Super Comp, Super Gas, and Top Dragster. In 1997, he set a record as the only driver to collect victories in four different categories in a single season, winning in Pro Stock, Super Stock, Competition, and Super Gas.
Coughlin entered the NHRA Powerade Drag Racing Series full-time in Pro Stock in 1998 and won the Rookie of the Year award. The following year he won five events and finished second in the championship standings. In 2000, he doubled his win total with 10 wins in 14 final-round appearances and claimed his first NHRA Pro Stock world championship.
His second championship came in 2002, when he won eight of the final 12 events of the season driving a Chevrolet. The 2003 season saw him finish in the top five while setting personal best speed and elapsed time records, and in 2001 he had set a national record for quickest elapsed time at Reading, Pennsylvania with a 6.750-second run.
Coughlin changed teams ahead of the 2005 season, joining Don Schumacher's operation and switching to Dodge Stratuses. After limited success in 2005, he won the season finale at Pomona, California, then took 2006 off from full-time professional competition. He returned in 2007 driving the JEGS-sponsored Chevrolet Cobalt for Victor Cagnazzi Racing and won his third NHRA Pro Stock championship that year.
In 2008, Coughlin collected three victories and four additional championship points milestones en route to his fourth Pro Stock title. He went to five final rounds during the season with three coming in the NHRA Countdown to One. After sitting out the 2011 season, he returned in 2012 driving a Dodge Avenger with Mopar and JEGS sponsorship.
On November 10, 2013, Coughlin secured his fifth Pro Stock championship after championship rival Jason Line lost in the second round at Pomona. The title made Coughlin one of the all-time leaders in Pro Stock championships. He debuted a JEGS.com/Mopar Dodge Dart at the 2014 NHRA Gatornationals, winning two of six final-round appearances that season.
Coughlin made three starts for Elite Motorsports in 2015, reaching a final in Seattle. He returned to full-time competition with Elite Motorsports in 2016, driving a Dodge Dart as teammate to Erica Enders. He continued competing for Elite Motorsports in subsequent seasons, piloting the SCAG Power Equipment / Outlaw Light Beer Pro Stock Camaro.
Coughlin is the only professional drag racer to have won from all 16 qualifying positions, a distinction that demonstrates both his driver skill and the breadth of starting positions from which he has converted final-round victories. He is also the only NHRA driver to win national events in four different categories in a single season (1997). His combined professional and Sportsman win total stands at 46 across his career. He is a five-time NHRA Pro Stock world champion (2000, 2002, 2007, 2008, 2013) in addition to his 1992 Super Gas title.
Coughlin's father, Jeg Coughlin Sr., founded JEGS High Performance, one of the largest aftermarket automotive parts retailers in the United States. The JEGS brand served as a longtime primary sponsor for Jeg Jr.'s racing program and remains closely associated with the Coughlin family's involvement in motorsport.