Hartley kept his ties with the American racing scene driving again for Starworks Motorsport in the 2014 and 2015 Daytona 24 Hours. In the 2016 Daytona 24 Hour he drove with Ford Chip Ganassi Racing. This tie saw him invited to drive for Chip Ganassi's Indycar team in 2018 but he had to decline due to securing a drive in Formula One with Toro Rosso. The 2017 WeatherTech SportsCar Championship saw him do three rounds for Extreme Speed Motorsports driving a Nissan Onroak DPi culminating in a victory at the 2017 Petit Le Mans.