The 31-year old Englishman was recently on a two-week trial with United and has now penned a deal which will keep him on the Gold Coast for the 2010/11 season.
Gold Coast coach Miron Bleiberg said the signing of Curtis was a major coup for the club.
“John impressed everyone with his skill, agility and attitude during his short time with us last month,” Bleiberg said.
“He is a quality player with a great pedigree and will be a big asset to us. His experience and knowledge will not only boost the team as a whole, but will also be a huge benefit to our younger players.
“We’re delighted that he has agreed to join us and I’m sure he will be a big success here.
“John is a specialist in the right full-back position and that’s exactly what we’ve been looking for. He also has a sharp football brain and can adjust very well if we need to alter our tactics during a game.
“I felt last season we were missing someone who was a natural right full-back. After watching him work I am confident that we have now found the right player to fill that role for us.”
During his extensive career which began with Manchester United in 1995, Curtis has played with Barnsley, Sheffield United Leicester City, Portsmouth, Preston North End, Nottingham Forest, Queens Park Rangers, Worcester City, Wrexham and won a League Cup with Blackburn Rovers in 2001/02.
Most recently he played with Northampton Town in England’s League Two and back in the late 1990s, represented the England U20 and B teams.