The 32-year-old free agent has penned a short-term deal at Victoria Road until the end of the season, coming just hours after the loan arrival of goalkeeper Jonathan Miles from Tottenham.
Fortune rose through the ranks at Charlton and spent more than a decade at the club before leaving for Sheffield United in 2009, returning to The Valley 12 months later for another season-long spell with the Addicks.
The experienced defender spent the second half of last season at Exeter before last summer joining Barnet, with whom he parted ways in January.
Interim boss Wayne Burnett told the Daggers' official website: "Jonathan Fortune brings a vast amount of experience to Dagenham and Redbridge Football Club.
"We are light with defenders so he will add depth to our squad. He comes with Premiership experience and I'm sure he will be a valuable asset to the team."