Nix, a four-star prospect from Pinson, Alabama, is the son of former Auburn quarterback Pat Nix, who played for the Tigers from 1992 to 1995.
"Obviously, it's a dream come true,'' Bo Nix said. "I've always wanted to play quarterback at Auburn. It's a goal of mine that I've had for a long, long time, as far as I can remember. All the way back to throwing the football in the backyard with my dad, I wanted to play quarterback at Auburn. So it was just an awesome moment. You honestly couldn't write it any better.''
Nix, who enrolled early in January, beat freshman Joey Gatewood for the job. Gatewood, a former four-star prospect, redshirted last season.
Coach Gus Malzahn informed the team of his decision earlier Tuesday.
"I think he had a very good fall camp,'' Malzahn said Tuesday evening. "I think there's a lot of intangibles that go with that. But at the end of the day, it's just the consistency and giving us the best chance of being successful.''
Nix won back-to-back state championships at Pinson Valley High School and set state records during his prep career with more than 12,000 total yards and 161 total touchdowns.
He is the first true freshman to earn the starting job during Malzahn's six seasons at Auburn.
"He's not your normal freshman,'' Malzahn said.
No. 16 Auburn opens the season against No. 11 Oregon and its star quarterback, Justin Herbert, on Aug. 31 at AT&T Stadium in Arlington, Texas.
The Associated Press was used in this report.