Williams averaged 14.7 points, 3.2 rebounds and 2.4 assists last season as the Aggies reached the Sweet 16. She was a second-team all-SEC honoree in 2016-17 after averaging 16.6 points per game.
"She is a seasoned basketball player who will immediately bring some maturity and experience to our backcourt," Texas coach Karen Aston said in a statement. "She is a gym rat also, which I think fits with our players, and is a sponge when it comes to wanting to be the best she can be in all areas of her life. Danni clicked with our players and staff from the start, and it seemed like it was a perfect fit."
In a statement, Williams thanked Aston and said she "can't wait" to start working with her Longhorns teammates.
Texas finished 28-7 last season, reaching the Sweet 16 before losing to UCLA.