Early career

Truex's father, Martin Sr., was a former champion in the Busch North Series and a successful modified driver. The younger Truex began racing in the Busch North series in 2000, and won 3 races in 3 years with a family owned team.

Truex rented a home from Dale Earnhardt, Jr. in Mooresville, North Carolina before he purchased his own home. His cousin, Curtis Truex, Jr., races modifieds at Wall Township Speedway and currently drives late-model stock cars in the southeatern U.S. for JR Motorsports, which is owned by Dale Earnhardt Jr..

Truex made his Busch Series start in 2001 at Dover International Speedway in his father's #56 XST Paintable Silicon Chevy. He started 19th but finished 38th after an early wreck. In 2002, Truex drove one race for Phoenix Racing at New Hampshire International Speedway, starting thirteenth but finishing 29th. He ran three races the rest of that season for his father, his best finish seveneenth at Dover.

NASCAR career

Busch Series

In 2003, he began the season with his father's team, before he was hired by Dale Earnhardt, Jr. to drive his #81 Chance 2 Motorsports Chevy. He made his debut with Chance 2 at Richmond International Raceway, where he qualified sixth and led eleven laps before transmission failure forced him to a 31st place finish. He split time between Chance 2 and his father's team for the balance of the season, except at Dover, where he drove for Stanton Barrett. He had a sixth-place run at Bristol Motor Speedway, and ended the season with two consecutive second-place finishes. He ran a total of ten races that season.

Truex raced full time for Dale Jr. in 2004. At Bristol Motor Speedway, he would earn his first career victory, and he would later add 3 more victories over the next 7 races. This would include a victory at Talladega Superspeedway which broke his car owner's streak of winning restrictor plate races in the Busch Series, and a victory at the final NASCAR event held at Nazareth Speedway. He took the lead in the championship after Nazareth, but lost it to Kyle Busch a few races later. However, a series of top 5's and top 10's in the second half of the season would allow Truex to pull away from Busch, clinching the Busch Series championship with a race to spare. While on his way to that championship, Truex made an appearance in Nextel Cup as a relief driver to Dale Jr., who'd suffered burns in a sports car accident. Truex started his first career Cup race for Dale Earnhardt, Inc. at Atlanta Motor Speedway later that year, qualifying 33rd and finishing 37th.

Truex stayed in the Busch Series to defend his championship in 2005, winning the title for the second season in a row. He won the first NASCAR race held in Mexico, as well as defending his Busch wins at Talladega and Dover International Speedway. He took his first win at Daytona International Speedway on July 1st, 2005.

2006

Truex ran full-time in the 2006 NEXTEL Cup season in the #1 Bass Pro Shops Chevrolet for Dale Earnhardt, Inc. He finished in the top 10 five times and finished the 2006 season 19th in points. Coming off of two consecutive Busch Series championships, Truex was widely considered to be a contender in the NEXTEL Cup Series. However, by his own admission, Truex's 2006 season had been somewhat disappointing. He was behind fellow rookies Denny Hamlin (who finished 3rd in points) and Clint Bowyer (who finished 17th in points). However, at 19th, he still had a respectable position for a rookie driver. Furthermore, Truex had a better later part of the 2006 season. He experienced a turnaround of sorts, finishing 6th, 11th, 5th and 2nd at Dover, Kansas, Talladega and Homestead, respectively. In 2006, he also made six starts in the Busch Series for Earnhardt, winning at Talladega.

2007

On May 19, 2007, Martin won the NASCAR Nextel All-Star Open, securing a spot in the Nextel All-Star Race, where he finished 10th.

On June 4th, 2007, Martin Truex Jr. won the Autism Speaks 400, scoring his first career Nascar Nextel Cup series win. With an interval of 7 seconds on pole sitter Ryan Newman. Truex Jr. led over half of the race (219 of 400 laps).