McKinnie signed with the Raptors prior to the 2017-2018 campaign. He was shuttled back and forth between the G-League and the NBA. He appeared in 14 games for the Raptors during the regular season. Essentially a 25-year-old rookie, McKinnie played 3.8 minutes per contest. He averaged 1.5 points and 0.5 rebounds per game. McKinnie shot 53.3-percent from the floor. He scored a season-high nine points at Denver on Nov. 1. He also tallied two rebounds and one block in nine minutes played in that contest, arguably his best game of the season. McKinnie collected two points, one rebound and one assist at Atlanta on Nov. 25. He registered one steal against the Brooklyn Nets on Dec. 15.

Moving from Toronto to Golden State, McKinnie saw his numbers rise across the board in his first season with the Warriors. He immediately served as a valuable reserve option for Golden State throughout the 2018-19 season and production quickly followed. Over the course of the first 16 games of the season, McKinnie averaged 6.3 points and 3.8 rebounds over 16 minutes per contest. McKinnie scored in double figures on three separate occasions during that time frame, including a 19-point, 10-rebound double-double in a win over the Bulls on Oct. 29. During a four-game stretch from Nov. 2 to Nov. 10, McKinnie averaged a whopping 26 minutes per night. A foot injury cost McKinnie nine games worth of action from late November to early December, but he didn't miss a beat upon his return. In his first five contests following the setback, McKinnie posted 6.2 points and 5.2 rebounds in 17.4 minutes per game. Having earned the trust of coach Steve Kerr, McKinnie saw playing time in all 22 of Golden State's postseason contests. That included a 12-point effort in a two-point win to help close out Portland in Game 4 of the Western Conference Finals. Overall, per 36 minutes last season, McKinnie averaged an impressive 12.1 points and 8.9 rebounds.