The Ford GT40 Mk1's (chassis 101 and 102) first made their appearance at the LeMans test weekend, April 18-19 in 1964. The car suffered from aerodynamic problems, and one of the cars even crashed after becoming airborne on the Mulsanne straight. The Mk1's made their debut race at the Nurburgring 1000 Kilometers in May of that year. The car ended up dropping out of the race due to suspension failure. Three Mk1's were entered in the 24 Hours of LeMans in 1964. Although none of the cars finished the race (2 gearbox failures and a ruptured fuel line), Phil Hill set a lap record in his Mk1.

In 1965, with the racing program taken over by Shelby American, the Mk1 raced at Daytona, Sebring, Monza, and the Nurburgring. The Mk1's first victory was recorded in the Daytona Continental on February 28th. The LeMans effort was stepped up for 1965 as well, with two Mk2 prototypes being entered along with the three Mk1"s. Once again, none of the cars finished the race due to blown head gaskets and gearbox problems. After LeMans, the Mk1 was left behind as development on the Mk2 was fully underway.