Nemechek began racing at thirteen in motocross and won approximately 300 races over six years. He made his Busch Series debut at North Carolina Speedway in 1989 and moved to full-time competition in 1990, winning Rookie of the Year honors. After sixteen top-ten finishes and sixth in the 1991 championship standings, Nemechek secured full-time sponsorship from Texas Pete sauce in 1992 and claimed the Busch Series title, defeating Bobby Labonte by just three points. He won his first two career races that season and later won the 1999 Cup race at Loudon for his first Cup victory. He made his Winston Cup debut for his own NEMCO team at New Hampshire in 1993.
Nemechek joined Larry Hedrick Motorsports for the 1994 Cup season, then moved his own team to Cup in 1995. In 1996, driving the No. 42 Bellsouth car for SABCO Racing, he experienced a devastating personal loss when his brother John was killed in an accident at Homestead-Miami Speedway. Despite this, Nemechek won the first two pole positions of his career that year and remained a competitive Cup presence through the late 1990s.
Driving for Andy Petree Racing in 2000, Nemechek achieved a career-best 15th-place points finish. After Petree's team ran into financial difficulties, Nemechek moved to Haas-Carter Motorsports in 2002. When Kmart's bankruptcy disrupted that team, he was hired by Hendrick Motorsports to replace the injured Jerry Nadeau in the No. 25 UAW-Delphi Chevrolet. He impressed enough to earn the ride full-time in 2003, and in that season won the rain-shortened Pontiac Excitement 400 at Richmond in dominant fashion — leading from the start and leading the most laps — before dedicating the win to Nadeau, whose career had been ended by a practice crash. Despite the victory, Nemechek was released at season's end in favor of Busch Series driver Brian Vickers.
Nemechek returned to MB2 Motorsports in 2004, driving the No. 01 U.S. Army car. In October that year he won at Kansas Speedway, beating out Ricky Rudd at the finish. Having also won the Busch Series race at Kansas the day before, he became the first driver to sweep the Busch-Cup double at that track. In 2005 a high-profile rivalry with Kevin Harvick drew attention after Harvick caused a multi-car crash involving Nemechek during Daytona 500 practice; the feud culminated in a heated post-race confrontation at The Nextel Challenge later that season. After MB2 was rebranded as Ginn Racing in 2006, Nemechek was released in mid-2007 due to lack of sponsorship.
Following stints with E&M Motorsports and Furniture Row Racing, Nemechek revived his NEMCO Motorsports team for 2009, running in both the Sprint Cup and Nationwide Series in the No. 87. Limited funding forced frequent "start-and-park" appearances — entering races, accumulating prize money, then retiring early to conserve parts. Despite these constraints, Nemechek competed across NASCAR's top three series for years and became notable for his sheer longevity.
On November 15, 2019, at ISM Raceway, Nemechek surpassed Richard Petty's record to become the driver with the most starts across NASCAR's three national series, reaching 1,186. The record stood until Kevin Harvick passed him in 2021. That same weekend at ISM Raceway, Nemechek and his son John Hunter became the first father-son duo to race in all three main NASCAR series over one weekend. Nemechek has also competed in historic motorsport events since 2021, winning the Gene Felton Memorial at Road Atlanta three consecutive times from 2022 to 2024.
Joe Nemechek's career spans more than three decades of NASCAR competition, anchored by his 1992 championship, two Cup victories, and an extraordinary record for longevity. His son John Hunter Nemechek competes full-time in the Cup Series for Legacy Motor Club, carrying the family name into the sport's current era.