The team announced the signing Monday.
McBath was a second-round draft pick by Denver in 2009. He played 20 games for the Broncos and started once. He had 28 tackles, two interceptions, and four passes defensed.
McBath was released by the Broncos last September and played one game in December for Jacksonville before being cut earlier in the offseason.
McBath is a former college teammate at Texas Tech of 49ers receiver Michael Crabtree. Also, his position coach his first two seasons with the Broncos was current 49ers secondary coach Ed Donatell.
The 49ers also announced linebacker Darius Fleming has been placed on the active/physically unable to perform list. Guard Joe Looney and running back Jewel Hampton have been placed on the active/non-football injury list.