The NBA named Booker as Lillard's replacement Thursday, one day after the Portland Trail Blazers star suffered a right groin strain.
Booker, 23, will make his first career All-Star appearance in his fifth season. The former Kentucky star is the NBA's 10th-leading scorer, averaging 26.4 points per game, and is the Suns' first All-Star since Steve Nash in 2011-12.
Booker was among the more notable snubs when the NBA announced its initial All-Star reserves last month. He acknowledged being disappointed.
"It was always a goal of mine [to be an All-Star], but it just reproves the point that the NBA is different than the game that I fell in love with at the beginning, [with] all the best players in the All-Star Game, growing up watching that," he said on Jan. 31. "And now it's an entertainment-, drama-, political-filled league."
Lillard was injured in the second half of Portland's 111-104 loss to Memphis on Wednesday night. He said after the game that he would not compete in either the All-Star Game or the 3-point contest.
Lillard also noted that he hoped Booker or "someone like that" would fill his spot.
Although this is his first All-Star Game, Booker has been part of All-Star Weekend in each of his five NBA seasons. He has been in the 3-point contest three other times, winning the title in 2018 and also competing in 2016 and 2019. He was a finalist in that event as a 19-year-old in 2016, alongside Golden State's sharpshooting duo of Klay Thompson and Stephen Curry.
Booker still holds the 3-point contest records for most points in any round and most points in a final round -- he had 28 points in the finals to win the title two years ago. Booker took part in the skills challenge in 2017.
He also scored 25 points in the 2016 Rising Stars game and 17 points when he returned to that game for first- and second-year players the following season.
The Associated Press contributed to this report.