Hunter-Reay began to compete in the IMSA Tudor United SportsCar Championship after the American Le Mans Series and the Rolex Grand-Am Sports Car Series merged in 2013. Hunter-Reay would drive for SRT Motorsports in the #91 Street and Racing Technology SRT Viper GTS-R-SRT 8.0 L V10 in the GTLM class. At the season-opening Rolex 24 at Daytona Hunter-Reay co-drove with Dominik Farnbacher and Marc Goossens. The car would qualify on the pole position in its class and in 24th place overall. The car would complete 675 laps to finish in 3rd place in its class and in 12th place in its class. Hunter-Reay then competed in the second race of the season, the Mobil 1 12 Hours of Sebring fueled by Fresh from Florida. Hunter-Reay drove the same car with the same co-drivers from Daytona. The car started in 10th place in its class and in 35th place overall. The car would complete 284 laps to finish in 7th place in its class and in 18th place overall. Hunter-Reay would compete in the season-ending Petit Le Mans presented by Mazda in the same car with Kuno Wittmer and Goosens. The car would start in 26th place and would finish in 11th place overall with 392 laps complete. The car would finish in 3rd place in its class. Hunter-Reay would finish in 19th place in the GTLM drivers championship with 87 points. The #91 SRT Motorsports entry would finish in 3rd place in the GTLM teams championship with 314 points.