A league source tells PFT that Manningham has agreed to terms with the 49ers on a two-year deal.
Manningham also had been in negotiations with the Rams.
The moves comes at a time when Peyton Manning is in the final days of selecting his next team. The finalists (for now) are the 49ers, Titans, and Broncos.
Manningham joins a depth chart that includes Michael Crabtree and Randy Moss.
The signing makes the Niners more dynamic on offense. Should Peyton Manning somehow lend up in San Francisco, the 49ers would become instant NFC favorites to reach the Super Bowl this season.