The 25-year-old Gaither, who missed the entire 2010 season with a back injury, made 28 starts in 33 games with the Ravens. He also started five playoff games with Baltimore.
The 6-foot-9, 350-pound Gaither was selected by the Ravens in the fifth round of the 2007 supplemental draft.
Gaither adds some experience to the Chiefs' offensive line.
Branden Albert has solidified one of the tackle spots, but Barry Richardson has struggled throughout the start of training camp at the other position. The Chiefs' only veteran backup is Ryan O'Callaghan.
Information from The Associated Press is included in this report.