LaJoie started in kart racing in 1996, winning 19 times on dirt and asphalt. He progressed through Bandolero, Legends cars, and the UARA-Stars Late Model Touring Series. In the NASCAR Camping World East Series, LaJoie scored five wins in 2012, including his first at Bowman Gray Stadium, and finished second in the points standings. He also won his first two ARCA Racing Series starts in 2013 at Chicagoland Speedway and Pocono Raceway.
LaJoie made his Sprint Cup Series debut in September 2014 at Loudon for Randy Humphrey Racing before spending several years working his way up through various underfunded operations. He returned to the Cup Series full-time in 2017 with BK Racing, where his qualifying move at Daytona — spinning out Reed Sorenson in the Can-Am Duels to secure the final open spot in the field — drew criticism from Sorenson and others in the paddock.
After a partial 2018 season with TriStar Motorsports, LaJoie joined Go Fas Racing's No. 32 Ford in 2019. He scored two top-ten finishes that year and logged a sixth at the Coke Zero Sugar 400 and a seventh at the 1000Bulbs.com 500 at Talladega. His 2020 season included a dramatic collision with the airborne Ryan Newman in the Daytona 500, an incident that dented LaJoie's windshield and briefly hospitalized Newman.
LaJoie moved to Spire Motorsports in 2021 on a multi-year deal. His most dramatic near-miss came at the 2022 Atlanta race, where he led with two laps remaining before Chase Elliott blocked him on the high side, causing LaJoie to brush the wall and spin from what appeared to be his first career win.
The 2023 season was LaJoie's most consistent in Cup competition: he finished 25th in points with no DNFs throughout the entire season, the only driver in the field to complete that mark. In 2024, LaJoie was involved in two separate Cup Series flips — at Talladega and Michigan — becoming the first Cup driver since Rusty Wallace in 1993 to flip twice in one season. After a career-best top-ten at the non-restrictor-plate track of Darlington, he departed Spire and moved to Rick Ware Racing.
LaJoie has built a parallel identity as a broadcaster and podcaster. He hosted Motor Racing Network's Sunday Money podcast and in 2021 launched his Stacking Pennies podcast on NASCAR.com. In 2025, he was announced as an analyst for Amazon Prime Video's Cup Series coverage alongside Danielle Trotta while continuing to race part-time. He has become one of the more recognizable non-winner personalities in the NASCAR garage due to his self-deprecating humor and willingness to discuss the financial realities of underfunded teams.
LaJoie's father Randy won back-to-back Busch Series championships in 1996 and 1997. LaJoie is a practicing Christian and remains deeply connected to the family motorsport tradition. His Stacking Pennies Performance brand, launched in 2025, reflects his entrepreneurial activity alongside his racing and media work.