Johnson tweeted Monday that "I'm excited to be a Yellow Jacket and looking forward to a great season."
Because he already has graduated, Johnson would be eligible to play for Georgia Tech next season.
Johnson announced two weeks ago that he had entered the NCAA transfer portal.
After starting all 12 games for Tennessee in 2018, Johnson made only three starts as a junior this season. He did appear in all 12 regular-season games for the Volunteers this year while playing both guard spots.
Last year, Johnson started one game at right guard and 11 games at center. He made four starts in 2017 while playing center, left guard and right guard.