The championship's direct lineage runs back to the IMSA GT Championship, founded in 1971, which operated through 1998. Through the late 1990s and into the 2000s, top-level North American sports car racing fragmented into two competing series: the high-technology-focused American Le Mans Series (ALMS), which followed ACO regulations aligned with the 24 Hours of Le Mans, and the cost-controlled Rolex Sports Car Series operated by Grand-Am Road Racing.
The two series merged in 2014 to form the United SportsCar Championship, announced on September 5, 2012. The merger was a complex undertaking: Grand-Am's Daytona Prototype category and IMSA's LMP2 class were consolidated into a single prototype category, while the two series' separate GT classes were rationalized into a combined structure. The class framework was unveiled on March 14, 2013 at Sebring International Raceway, two days before the 12 Hours of Sebring. The new series was named in a public contest won by Louis Satterlee of Florida.
Rolex's Tudor brand served as title sponsor in 2014 and 2015. WeatherTech became the title sponsor from 2016, giving the series its current name. The series was renamed simply the IMSA SportsCar Championship in 2016, though the WeatherTech title sponsorship is used universally.
The IMSA season opens with the Rolex 24 at Daytona in late January and concludes with the Petit Le Mans at Road Atlanta in early October. The calendar combines endurance events and shorter sprint races; only certain classes run at all rounds. Five events constitute the Michelin Endurance Cup sub-championship: the 24 Hours of Daytona, the 12 Hours of Sebring, the 6 Hours of Watkins Glen, the SportsCar Endurance Grand Prix, and the Petit Le Mans.
Television coverage in the United States is handled by NBC Sports properties. From 2019, the series moved to an exclusive deal with NBC Sports, with the broadcast NBC network airing nine hours of coverage annually and NBCSN (later replaced by USA Network from 2022) providing additional coverage.
The championship operates four classes. The Grand Touring Prototype (GTP) class is the flagship category, introduced in 2023, featuring cars built to IMSA's LMDh regulations or the ACO's Le Mans Hypercar specifications, aligning North American prototype racing directly with the FIA World Endurance Championship machinery. The Le Mans Prototype 2 (LMP2) class, a separate category since 2019, features ACO-homologated LMP2 cars with pro-am driver lineups limited to one gold-rated driver per entry.
In the grand touring classes, the GT Daytona Pro (GTD Pro) category uses FIA GT3-specification cars with no driver rating restrictions, introduced in 2022 to replace the former GTLM class. The GT Daytona (GTD) class also uses GT3 cars but requires at least one silver- or bronze-rated amateur driver per entry. GTP, LMP2, and GTD are all compatible with ACO/FIA technical regulations, facilitating the participation of teams and manufacturers aligned with the Le Mans program.
Earlier iterations of the championship used a broader class structure. The Daytona Prototype International (DPi) class was the flagship from 2019 to 2022, using cars based on LMP2 platforms with manufacturer-specific bodywork. Prior to DPi's introduction, the unified Prototype class (2014–2018) combined Grand-Am's Daytona Prototypes with ALMS-derived LMP2 cars. The Prototype Challenge class used the spec Oreca FLM09 car from 2014 to 2017, while an LMP3 class ran from 2021 to 2023 before transitioning to the IMSA VP Racing SportsCar Challenge support series. The GT Le Mans (GTLM) class, matching ACO GTE specification, competed from 2014 to 2021.
The IMSA WeatherTech SportsCar Championship is the definitive measure of North American sports car racing, consolidating a fragmented landscape into a single cohesive series. Its alignment with ACO and FIA regulations through the LMDh and LMP2 frameworks means its top classes run machinery shared with the FIA World Endurance Championship and the 24 Hours of Le Mans, elevating the competitive and commercial stature of the series to a globally relevant level.