In 2010, he made his first start in the preseason finale against the Miami Dolphins, leading the Cowboys to a 27–25 victory, while completing 27 of 42 passes for 304 yards, one touchdown, and no interceptions. He began the season as the third-string quarterback and was declared inactive in the first six games. In the sixth game against the New York Giants, starter Tony Romo was lost for the season with a broken left clavicle. McGee was promoted to second-string quarterback behind Jon Kitna for the next 9 games. In the Christmas Day game against the Arizona Cardinals, McGee replaced the injured Kitna in the second half, and made his first regular-season touchdown pass to wide receiver Miles Austin. The touchdown gave the Cowboys a 26–24 lead with 1:47 remaining, but the Cardinals soon scored a field goal to win 27–26. McGee recorded 11 of 17 passes for 111 yards, no touchdowns, and a quarterback rating of 102.8. In the season finale against the Philadelphia Eagles, McGee started his first NFL game. He went 11-of-27 for only 127 yards, and threw a touchdown pass to tight end Jason Witten with 55 seconds left to give Dallas a 14-13 victory over their divisional rival.