With Tuesday's announcement, San Francisco has all 11 of its draft picks signed. The former LSU safety actually had tweeted a photo from Instagram of him signing a contract last week.
Financial terms of the deal were not disclosed. The 49ers drafted Reid 18th overall in April.
In 39 games over three seasons with LSU, the 6-foot-1, 213-pound Reid finished with 199 tackles, six interceptions, two forced fumbles, two fumble recoveries, 11 pass breakups and 4½ tackles for loss. Last season, Reid started all 13 games and tallied 91 tackles, two interceptions, one fumble recovery and seven pass breakups.
The 22-year-old is a native of Baton Rouge, La.