The 27-year-old joins the Shrimpers as a free agent after being released by Aldershot at the end of last season.
Reid, who started his career with Coventry, has also enjoyed spells with Cheltenham and Newport.
"I'm pleased to have signed a deal with Southend United and I can't wait to get started," he told the club's official website.
"Last season was tough with everything that went on at Aldershot but I'm very happy to be back in the Football League with Southend and hopefully we can have a successful season.
"Hopefully I can score goals and show the fans what I can really do. I can't wait for the season to get started against Plymouth on Saturday."