The league made the milestone official Tuesday ... saying Thomas will serve as the down judge for S.B. LV.

Of course, Thomas has been an official in the NFL for 6 seasons ... and has four playoff games under her belt. She also broke the playoff barrier in 2015, when she became the first female to officiate a postseason game.

The league released a statement on the accomplishment ... saying Thomas's "elite performance and commitment to excellence has earned her the right to officiate the Super Bowl."

"Congratulations to Sarah on this well-deserved honor."

Tennis legend Billie Jean King also congratulated Thomas on the achievement, saying, "Keep breaking those barriers, Sarah."

FYI, the decision is anything but a publicity stunt -- It’s awarded to the highest-rated person at their position and is selected over the course of the 2020 season.