The Lakers announced the deal Thursday.
Holmes spent the past four seasons at Texas, averaging 10.3 points and 6.1 rebounds per game as a senior. He plays a versatile two-way game, with a solid 3-point shot and strong defensive instincts.
After going undrafted, Holmes averaged 12.2 points and 5.6 rebounds for the Boston Celtics' entry in the NBA Summer League in Las Vegas last month.
Holmes will compete for a roster spot in training camp with the rebuilding Lakers, who are coming off the worst season in franchise history. Los Angeles drafted D'Angelo Russell, Larry Nance Jr. and Anthony Brown in June, while 2014 first-round pick Julius Randle is returning from injury.