IROC launched in 1973 with a field of 12 invited drivers competing in identically prepared stock cars maintained by a single team of mechanics. The intent was to eliminate equipment advantages entirely, making the outcome a pure test of driver skill. The inaugural champion was Mark Donohue, who won the title in 1974 after the four-race series concluded. The cars used in that first season were Porsche Carrera RSRs. Donohue's win in the fourth and final race of the inaugural season proved to be the last victory of his career; he died following a crash in practice for the 1975 Austrian Grand Prix at the Österreichring.
Drivers were invited based on their recent accomplishments — typically season champions of major series or winners of marquee events such as the Indianapolis 500 or the Daytona 500. Criteria remained deliberately loose throughout the series' history.
IROC became recognized for a distinctive color-coding system used in place of conventional numbering. Through 2003, cars were painted in vivid, contrasting colors with the driver's surname on the door rather than a number. Car numbers were used for scoring but not as the primary identifier. Numbers were assigned by starting position for the first race of each season, then adjusted based on finishing order or points standings for subsequent races. Starting positions were determined by blind draw, with the finishing order of each race inverted to set the following race's grid.
Notable exceptions were made for drivers sharing a surname: when Mario and Michael Andretti competed in the same event, first names were used instead. After the death of Dale Earnhardt in the 2001 Daytona 500, IROC retired the use of car number 3. Any driver whose regular series number was 3 used 03 instead, including Helio Castroneves.
In 2004, Crown Royal (a Diageo brand) replaced True Value as title sponsor and the identification system changed. Cars were painted identically in white with team-colored trim matching each driver's regular series livery, and each driver ran their usual series number in IROC.
From 1973 to 1991, the IROC schedule included at least one road course event each season. Riverside International Raceway hosted the most IROC road races, followed by Watkins Glen International. Races were also held at Mid-Ohio, the Daytona road course, and the temporary Cleveland street circuit used by CART.
From 1992 through 2005 the schedule was exclusively ovals. Road courses were reintroduced in 2006 when the cars competed on the infield road course at Daytona International Speedway. That same year, Grand-Am endurance drivers Max Angelelli and Wayne Taylor shared a single IROC entry, combining their points in a unique team format that reflected sportscar racing's co-driver tradition. The format was not repeated.
Despite the series' stated goal of equal competition across disciplines, IROC was routinely dominated by NASCAR drivers. The proportion of NASCAR invitees in the 12-car field grew steadily over time — from three drivers in the first season to seven in the final season. The last champion from outside a NASCAR background was Al Unser Jr., who won the title in 1988. Open-wheel and road racing drivers achieved individual race victories but rarely sustained championship challenges.
Mark Martin became the all-time leader in IROC championship titles with five and in race victories with thirteen, both records established during the 2005 season when the series ran for the final time.
Several championship seasons were marked by tragedy. In 1993, Davey Allison was killed in a helicopter crash after three of the four races were complete. Terry Labonte was invited to drive the final race, and Allison was awarded the championship posthumously based on combined points; Labonte's prize money was directed to a trust fund for Allison's children. Alan Kulwicki had also been killed earlier that same year in a plane crash, with Dale Earnhardt chosen to complete the field in Kulwicki's place, with all winnings going to charities designated by the Kulwicki family. After Earnhardt's death in the 2001 Daytona 500, the series ran with an 11-car field for the remaining three races of that season.
In 2007, IROC failed to secure a title sponsor and postponed the opening two rounds at Daytona and Texas before going on hiatus with hopes of returning in 2008. That return never materialized. In March 2008, IROC auctioned off its cars, tools, and equipment, formally dissolving the series.
IROC's legacy persisted in multiple forms. During the COVID-19 pandemic in 2020, drivers from NASCAR, IndyCar, NHRA, IMSA, and Formula One competed in an iRacing event explicitly framed as a tribute to IROC. In 2021, final IROC champion Tony Stewart and Ray Evernham launched the Superstar Racing Experience (SRX), directly applying the IROC concept of identical cars and cross-discipline all-star fields. On January 8, 2024, Evernham and Rob Kauffman announced plans to relaunch the IROC brand itself, with one event in 2024 and exploration of future opportunities.