Nemechek began his racing career at the age of 5, competing in go-karts, quarter midget cars and in dirt bike competition. He moved up to stock car competition in 2010, competing in the Allison Legacy Series with sponsorship from England Stove Works. In 2012, Nemechek moved up to late model and super late model competition, competing in the Champion Racing AssociationSuper Series and American Speed AssociationMidwest Tour; he also competed in the World Series of Asphalt at New Smyrna Speedway during Speedweeks. Nemechek won praise from Sprint Cup Series driver Kyle Busch following a CRA Super Series race in which both drivers competed. In June 2012, Nemechek won the pole for the Howie Lettow Memorial 150, an ASA Midwest Tour event, at the Milwaukee Mile; he was scheduled to take a driver's education course the following week as he had just passed his fifteenth birthday. He finished 23rd in the event. After competing in the 2012 Snowball Derby, starting second and finishing tenth, Nemechek won the 2012 Allison Legacy Series championship, winning 15 of the season's 18 races. In 2013, Nemechek moved to competing in the Southern Super Series as well as in selected races in the NASCAR K&N Pro Series East, starting with the UNOH Battle at the Beach at Daytona International Speedway in February. In late 2013, he made his debut in the Camping World Truck Series, driving the No. 22 Toyota for SWM-NEMCO Racing. He competed in two events, with a best finish of 16th. In January 2014, Nemechek announced he would be competing in ten Camping World Truck Series events during the 2014 season. After the season ended, he won the 300-lap Snowball Derby. On September 19, 2015, 16 years to the day his father won his first Cup race, Nemechek won his first Truck Series race at Chicagoland. On November 29, Nemechek has voted the Most Popular Driver for the 2015 season in the Truck Series. In 2016, Nemechek won at Atlanta. At Canadian Tire Motorsport Park during the 2016 Chevrolet Silverado 250, Nemechek and Cole Custer were battling for the lead when Nemechek bumped Custer which led to Nemechek losing control and intentionally sending both Custer and himself off-road, pinning Custer to the wall. Before the winner was declared, Nemechek was tackled by Custer; Nemechek would be named the winner. In 2017, Nemechek won back-to-back races at Gateway and Iowa. Nemechek missed the Championship Four after finishing 2nd at Phoenix. For the 2018 season, Nemechek joined Chip Ganassi Racing to drive the No. 42 NASCAR Xfinity Series car on a part-time basis. He also would continue to run select Camping World Truck Series races for his father's team NEMCO Motorsports. He would win at Martinsville in March. He suffered heartbreaking losses at Chicago and Bristol, after running out of fuel on the final lap in Chicago, handing the win to Brett Moffitt, and suffered fuel pickup issues with 5 laps remaining and a 2-second lead in Bristol, allowing Johnny Sauter to take the lead and eventual win. Nemechek would go on to finish 7th and 3rd in those races, respectively. In his Xfinity Series debut, Nemechek finished an impressive 4th-place finish at Atlanta, though he was involved in an early race wreck involving Elliott Sadler and Cole Custer resulting in Custer's car wrecking. Nemechek followed up the 4th-place run with a 29th-place finish at Auto Club after a tire failure ruined his chances of a good run. His next Xfinity Series races were the four Dash 4 Cash races, where he had one top ten finish at Talladega. On October 20, 2018, after dominating the race and winning stage 2, Nemechek won his first career Xfinity race at Kansas Speedway in the 2018 Kansas Lottery 300. In 2019, Nemechek signed with GMS Racing for the full Xfinity schedule in the No. 23 Chevrolet. On October 29, Front Row Motorsports announced that Nemechek would fill in for Matt Tifft in the No. 36 Ford for the final three races of the 2019 Monster Energy NASCAR Cup Series after medical issues forced Tifft from the ride. Nemecheck and his father Joe made motorsports history at ISM Raceway in early November 2019 by being the first father-son duo to race in all three main series in one weekend. He finished the 2019 season seventh in points after finishing sixth at Homestead. On December 12, 2019, Front Row Motorsports announced that Nemechek will replace David Ragan as the driver of the No. 38 Ford for the 2020 season. He will also compete for the 2020 NASCAR Rookie of the Year honors.
