Harris, 32, started 10 games last season after Ray Lewis suffered a season-ending shoulder injury, collecting 73 tackles, two sacks and two interceptions.
The 6-foot-2, 250-pounder closed the season with nine tackles, three pass deflections and one sack in a 34-31 loss to the Pittsburgh Steelers.
A former starter for the Green Bay Packers' 1996 Super Bowl champion squad, Harris reportedly agreed to a $680,000 contract that includes a $25,000 signing bonus.
With the free agent losses of quarterback Jeff Blake, fullback Sam Gash and receiver Brandon Stokley who signed with Arizona, Buffalo and Indianapolis, respectively, as well as the unsigned status of defensive backs Robert Tate and James Trapp and return specialist Jeff Ogden, the Ravens have re-signed six of their 12 unrestricted free agents.
Trapp, who intercepted three passes, is the most likely to return of those remaining three unrestricted free agents. His agent, George Mavrikes, said Trapp has drawn fleeting interest from Tampa Bay and thought any deal with Baltimore was more likely to happen after the NFL Draft.