The deal is worth up to $3.75 million with incentives, sources tell ESPN NFL Insider Adam Schefter. DeCoud will get a $500,000 signing bonus.
DeCoud, 29, was a Pro Bowler for the Falcons in 2012. He started all but two games for Atlanta over the past six seasons, intercepting 14 passes while recording 507 tackles.
"Thomas provides a veteran in the secondary who is familiar with the NFC South and has been a very solid player," Panthers coach Ron Rivera said in a statement. "We are pleased to add him to a safety group that has good experience and production."