Jim Vertuno of the Associated Press reported the two additional years include $13.25 million in guaranteed money.
Texas had endured three consecutive losing seasons before it hired Herman away from the University of Houston in November 2016.
The Longhorns alum led the program to a 7-6 record with a victory in the Texas Bowl in 2017. They improved to 10-4 during a 2018 season that was capped by winning the Sugar Bowl and being ranked No. 9 in the final AP and Coaches' polls.
It was the highest final ranking for Texas since 2009.
The 43-year-old Ohio native said the 2019 version of the Longhorns can't get caught up in last year's success, though.
"Last year's team will never be referred to as 'we' or 'us,'" Herman told reporters in April. "We didn't win the Sugar Bowl. That was last year's team. We have a lot of work to do. But those of us that were on last year's team can certainly learn some lessons from it."
The next step is getting the Horns back into national championship contention. The progress toward that goal continued by signing the third-best 2019 recruiting class in 247Sports' composite rankings.
Texas opens the new season Aug. 31 against Louisiana Tech.