Claxton was selected with the 31st overall pick in the 2019 NBA Draft by the Nets. The Georgia product made his NBA debut Nov. 8 in a win over the Trail Blazers, recording eight points (3-5 FG, 2-5 FT), six rebounds and one assist in 12 minutes. The 6-foot-11 big man had his first double-digit scoring outing on Jan. 18 against the Bucks, recording 14 points (7-12 FG), six rebounds (career high), three blocks (career high) and one assist in 19 minutes. He followed that up with what would end up being a career-high 15 points (6-8 FG, 1-2 3Pt, 2-3 FT) just two days later against the 76ers. In that contest, Claxton also recorded four rebounds and two assists in 17 minutes. The rookie played his final NBA game of the season Feb. 28 against the Hawks, recording four points (1-2 FG, 2-2 FT) and one rebound. On Jun. 24, Claxton had shoulder surgery which forced him to him to miss the resumption of the season that occurred after the COVID-19 sports stoppage. Claxton's NBA averages in his rookie campaign were 4.4 points, 2.9 rebounds and 1.1 assists in 12.5 minutes per game across 15 appearances. He also shot 56.3 percent from the field. The rookie also appeared in nine games for the G League Long Island Nets. With Long Island, Claxton posted 16.7 points, 7.3 rebounds, 1.8 assists, 1.2 blocks and 1.1 three-pointers over 21.3 minutes per G League contest.