In his second season in the Association, Giles appeared in 38 of 64 possible games for Sacramento with 17 starts. He made his season debut on Nov. 8 tallied four points, one rebound and one block over eight minutes of run. On Jan. 7, Giles received his first NBA start and delivered eight points, eight rebounds and a steal in 16 minutes of playing time. Come February, Giles was a regular starter. He was in the starting rotation in 14 of Sacramento's last 16 games before the season was suspended on Mar. 11. Over that span, Giles tallied 10.4 points, 6.3 rebounds, 1.3 assists and 0.6 steals over 21.0 minutes per game. Twice in February Giles grabbed a career-high 12 rebounds. On Feb. 22, Giles double-doubled via 14 points, 12 rebounds and two assists during a road win over the Clippers. Five nights later, the 21-year-old scored a season-high 19 points, with eight rebounds, during a close loss at Oklahoma City. Giles had 11 games with at least one block. He grabbed five or more boards in 12 contests. A knee injury forced Giles to miss first eight games of the season.

After sitting out the 2017-18 season to improve the strength in his knees, essentially taking a redshirt season, Giles made his NBA debut in the 2018-19 season. The Kings gradually increased his workload as the year went on, as he averaged 9.7 and 9.4 minutes per game in November and December, respectively, before seeing his playing time jump to 16.6 minutes per game in January, 15.3 in February, and 18.6 in March. The former 20th-overall pick was then shut down in April as a precaution. Overall, the 20-year-old averaged 7.0 points and 3.8 rebounds over 14.1 minutes per game. Giles recorded his first double-digit scoring effort on Nov. 12 against the Spurs. Later in the month he had back-to-back 10-point nights against Golden State on Nov. 24 and Utah on Nov. 25. He scored a season-high 20 points against Atlanta on Jan. 30 while also adding seven rebounds and one assist. Giles recorded a season-high nine rebounds in 18 minutes in a 119-116 win against Oklahoma City on Feb. 23. He scored in double-digits on three consecutive games twice, from Feb. 4-8 in games against the Spurs, Rockets and Heat, and again from Feb. 27-March 4 against the Bucks, Clippers and Knicks. His totals were especially impressive on a per-36 minute basis, where he averaged 17.9 points, 9.7 rebounds and 4.8 assists.