Abbas spent last season playing for the Pohang Steelers in Korea and will add to his 128 A-League caps when the season gets underway in October.
He will join initially as an injury-replacement player for Louis Fenton.
The 2007 Asian Cup winner said he was thrilled to return to Australia.
“After Korea there were many offers, a lot from home in Iraq, but I wanted to come back to the A-League,” he said.
“I’m really happy to be here, we have a really good squad. I just want to do my best, and to show the fans of Wellington that I deserve to keep playing at a high level, and hopefully it’s a long stay.”
Abbas, who was born in Iraq, has only spent one year abroad since joining the Marconi Stallions in 2008 and has become an Australian citizen in that time.
Newly appointed Phoenix boss Darije Kalezic was understandably pleased with Abbas’ signature.
“I am very happy with the group that we have recruited but also the players that we have retained,” he said.
“It hasn’t always been possible in the past to attract top-quality Australian players to join us here at Wellington – that has changed.”
Abbas adds to the already impressive list of Phoenix acquisitions, joining the likes of Scott Galloway, Daniel Mullen, Goran Paracki, Andrija Kaludjerovic and Dario Vidosic in the New Zealand capital.