Long began racing in 1983 at Orange County Speedway and South Boston Speedway. He won the track championship at South Boston in 1987 and the Street Stock championship at Orange County in 1990. In 1992 he entered NASCAR-sanctioned competition for the first time, winning the Rookie of the Year award at Orange County in the Winston Racing Series. He received the Best Sportsmanship award there the following season.
After competing at various Winston Racing tracks through the 1990s, Long stepped up to the Slim Jim All Pro Series in 1997, winning at Bristol Motor Speedway in the No. 15 Austin Foods Chevrolet. In 1998 he began running ARCA and Craftsman Truck races for Mansion Motorsports.
Long made his Cup Series debut in a qualifying attempt during 1999 before finally making the field at Dover in 2000, where he started 42nd and finished 41st after a crash on lap twelve. In a notably selfless gesture that year, Long gave up his qualifying spot for the Coca-Cola 600 to Darrell Waltrip, who was retiring at the end of the season and was denied a spot by a tenths-of-a-second margin.
Long spent the early 2000s competing as a rotating independent across Cup, Busch, and Truck Series events for a variety of small teams, rarely qualifying consistently but persisting through the field. A frightening accident at the 2004 Subway 400 at North Carolina Speedway saw his car flip multiple times; he was uninjured.
In May 2009, Long's engine at the Sprint Showdown was discovered to be 0.17 cubic inches over the regulation displacement limit during practice. NASCAR levied a $200,000 fine against Long — the largest in the sanctioning body's history to that point. Beyond the monetary penalty, Long and his team were docked 200 driver and 200 owner points and suspended for twelve Cup Series races, with a ban from all NASCAR competition until August 18, 2009, and probation through December 31. Because Long was unable to pay the fine, he was barred from Cup Series participation for years afterward. The record was later surpassed in 2013 when Michael Waltrip Racing was fined $300,000.
In 2014, Long partnered with Derek White to form Motorsports Business Management, operating in the Nationwide Series under the MBM Motorsports banner. White was later arrested on smuggling charges, and since 2016 Long has owned MBM outright. The team competes part-time in NASCAR's Cup, Craftsman Truck, and ARCA Menards Series.
In May 2017, Long reached an agreement with NASCAR to return to the Cup Series garage and entered the No. 66 Chevrolet SS at the Go Bowling 400 at Kansas under MBM Motorsports. The paint scheme was modelled closely on the No. 46 car he drove prior to his 2009 ban, retaining green and yellow colours. An attempted sponsorship deal with a marijuana vaping manufacturer was blocked by NASCAR after Long misspelled the company's name in his submission.
Long is widely regarded as one of NASCAR's quintessential independent operators — a "working man's" competitor who financed his own racing career without family money or corporate sponsor backing. He also held mechanical and administrative roles at several teams, serving as a crew member at Front Row Motorsports, crew chief for Eric McClure, and Competition Director at Rick Ware Racing. Outside of racing, Long was previously a Domino's Pizza franchise manager in Raleigh/Durham, where he was named manager of the year in 1988 and set the location's record for most pizzas delivered in a single night.