Barnes declined his $25.1 million player option for the 2019-20 season, becoming an unrestricted free agent.
Sacramento acquired Barnes from Dallas at the trade deadline last season with the hopes of making him a long-term focus of a franchise core that includes guards De'Aaron Fox and Buddy Hield and forwards Bogdan Bogdanovic and Marvin Bagley III.
Barnes, 27, averaged 16.4 points and 4.7 rebounds between the Mavericks and Kings in 2018-19, shooting 42% from the field and nearly 40% on 3-pointers.
Joining Barnes on the wing in Sacramento will be veteran Trevor Ariza, who has agreed to a two-year, $25 million contract, sources confirmed to The Undefeated's Marc J. Spears.
In 43 games for Washington, Ariza, 34, ended up averaging 14.1 points, 5.3 rebounds and 1.2 steals.
News of Ariza's move was earlier reported by The Athletic.
The Kings have also agreed with guard Cory Joseph to a three-year, $37 million contract, according to multiple reports.
Joseph, 27, averaged 6.5 points and 3.9 assists in 82 games this past season with the Indiana Pacers. The eight-year veteran figures to serve as a backup in Sacramento behind star point guard De'Aaron Fox.
NBA free-agent contracts can't be officially signed until Saturday.