Sherman has previously told Josina Anderson of ESPN that the two sides were discussing a deal.
The 29-year-old corner was released by the Hawks on Friday after seven years with the organization. He earned four Pro Bowl selections and three First Team All-Pro nods while establishing himself as one of the most valuable defensive players in the NFL.
His 2017 campaign came to a premature end after suffering a ruptured Achilles, though. Pro Football Focus graded him as the No. 33 CB in the league before the health setback.
Kamara Is Taking on All Comers in Paintball
There's No Offseason for NFL Workout Warriors
Norman Goes on Shopping Spree for Detained Families
Hue Jackson 'Cleansed' Cleveland with Lake Erie Plunge
'Last Chance U 'Star Getting His NFL Shot
Is 44-Year-Old T.O. Working Out for a Comeback?
Eagles Drafted a 6'8", 346-Lb Rugby Player 😳
Happy 4-Year Anniversary to the 2014 NFL WR Class
One-Handed LB Might Be Draft's Biggest Badass
Mayfield's Journey to the Draft Ends Thursday
Ball Fam Has Nothing on the St. Browns 😏
NFL Stars Spending Their Offseasons Giving Back
Derrius Guice Runs from Difficult Upbringing
Harold Landry Is Draft's Best Pure Pass-Rusher
Which Teams Are the Best Fit for Dez?
Johnny Football Is BACK!
Quavo's Mega-Celebrity Flag Football Game
Meet the NFL's Next Alshon Jeffery
Tremaine Edmunds Is NFL Draft No-Brainer
Grading the Rams' Deal with Suh
Sherman told Tom Pelissero of the NFL Network what he was looking for as a free agent.
"Looking for a great fit," he said. "A team that has a great QB. Looking for somewhere I will be comfortable."
The Niners could fit the bill with Jimmy Garoppolo now in the mix at quarterback. San Francisco, which was 1-10 before he took over under center after coming over in a trade with the New England Patriots, won five consecutive games to close out the regular season.
Sherman's track record makes it an investment worth making for the Niners, who ranked 22nd in pass defense in 2017.