Mayer grew up with racing in his blood — his father Scott Mayer is a former IndyCar Series driver and founder of QPS Employment Group. Sam began competing in go-karts at the age of four. Despite his father's open-wheel background, Sam gravitated toward stock car racing in his preteen years. At fourteen, he spent a summer in Charlotte racing Legends cars, winning the Young Lions division of the Charlotte Motor Speedway Summer Shootout. He also won at Greenville-Pickens Speedway that year, becoming the track's youngest winner, and claimed a Midwest Truck Series race at Dells Raceway Park in his series debut.
Industry veteran Lorin Ranier connected Mayer with JR Motorsports for the 2018 CARS Tour season, where he earned one win and was voted Most Popular Driver. He also made limited ARCA and NASCAR K&N Pro Series East starts that year with MDM Motorsports, notching a top-ten in his ARCA debut.
In 2019, Mayer signed with GMS Racing for a full K&N East campaign. He scored his first series win at Bristol on April 6, leading every lap. He went on to win the 2019 K&N Pro Series East championship with four wins, becoming the youngest NASCAR champion at 16 years, 3 months, and 8 days — breaking Todd Gilliland's record from 2016 by more than two months.
The 2020 season brought even more success. Racing in both ARCA Menards Series and ARCA Menards Series East with GMS, Mayer swept a Bristol race night by winning both the Truck Series and ARCA events. He won the East finale at Five Flags Speedway to capture the 2020 East championship with an extraordinary average finish of 1.2 on the season. He also won the inaugural ARCA Menards Series Sioux Chief Showdown championship that year.
On September 15, 2020, JR Motorsports announced Mayer would drive for them part-time in 2021 and full-time in 2022. He took over the No. 1 car in 2022, replacing Michael Annett. His 2022 season featured memorable moments including a physical confrontation with Ty Gibbs following contact at the Martinsville spring race; Mayer finished seventh in points with a best result of second at Talladega.
The 2023 season was his breakout campaign. Mayer scored four wins — at Road America, Watkins Glen, Charlotte Roval, and Homestead — the latter two coming in the playoffs to propel him into the Championship 4 at Phoenix. He finished third in the final standings, firmly establishing himself as one of the series' elite competitors.
In 2024, Mayer continued his winning ways with victories at Texas (by just 0.002 seconds over Ryan Sieg, one of the closest finishes in Xfinity Series history), Iowa, and the Charlotte Roval. However, his playoffs were disrupted when his car was disqualified at Talladega after failing a post-race ride height inspection. That season also brought controversy: NASCAR issued Mayer a one-race suspension at season's end for intentionally wrecking Jeb Burton on the Martinsville cooldown lap.
On August 17, 2024, Mayer signed with Haas Factory Team to drive the No. 41 Ford in the NASCAR Cup Series starting in 2025. He began his Cup career promisingly, finishing second at the Daytona 500 season opener. He earned his first Cup win at Iowa, giving Haas Factory Team their first Cup victory and marking Ford's first win of the year.
Mayer is known for an aggressive, confrontational racing style that has produced both spectacular victories and high-profile on-track disputes. His rise through NASCAR's developmental pipeline was extraordinarily fast — from go-karts to the Cup Series main stage in under a decade, with multiple championship titles along the way. His father's sponsorship through QPS Employment Group provided crucial support throughout his development years. The combination of raw talent, family backing, and fierce competitive instinct has marked Mayer as one of American stock car racing's most compelling young prospects.