Both players announced their intentions to enter the draft without an agent in early April, and had until Wednesday to decide whether to return to school.
Holiday, a 6-foot-1 rising junior guard, played a supporting role behind Lonzo Ball last season, but still averaged 12.3 points and 4.4 assists off the bench while shooting 41.1 percent from 3-point range. With Ball, Bryce Alford and Isaac Hamilton all departing after last season, Holiday could become the go-to guy on the perimeter next season. He's the younger brother of New Orleans Pelicans guard Jrue Holiday.
"It goes without saying that we're thrilled to have Aaron back for his junior season," head coach Steve Alford said in a release. "He played a major role in our success last season, and we're going to rely on him in a big way as we move forward. He's a team-first guy and a high-character individual. Aaron's prepared to make even greater strides as a junior, and we can't wait to see him continue to develop."
Welsh was a consistent piece for UCLA in the frontcourt last season. The 7-footer has good touch from the midrange, and shot 58.5 percent from the field. He averaged 10.8 points and 8.7 rebounds as a junior.
"Thomas has worked hard all spring," Alford said. "We supported him testing the NBA waters and are excited to have him returning for his senior year. He simply continues to develop each and every season. Thomas will be one of the top centers in college basketball next year and, undoubtedly, has a great chance to be a first-round pick in next season's draft."
Neither player was projected to be drafted in next month's draft, but their return to Westwood ensures Alford won't have to replace an entire rotation with newcomers. Ball and fellow freshmen TJ Leaf and Ike Anigbogu all declared for the NBA draft after one season, while Bryce Alford and Hamilton were both seniors. Had Holiday and Welsh kept their names in the draft, Alford would have had to replace his top seven players from last season's 31-5 campaign.
UCLA is bringing in the nation's No. 3-ranked recruiting class next season, led by five-star prospects Jaylen Hands and Kris Wilkes, and ESPN 100 big men Cody Riley and Jalen Hill. The Bruins are also heavily involved with five-star senior M.J. Walker, who will announce his commitment on Wednesday.