Adelaide's football director, Michael Petrillo was delighted with the signing.
"We're very pleased to be able to announce the signing of Iain Fyfe. To be able to pick up a player who has played in a winning championship side with Sydney FC, had Asian Champions League experience and still be only 26 years of age, was definitely one of the reasons we signed him," Petrillo said on behalf of coach Aurelio Vidmar.
"He is a proven winner, a terrific young man and there is no doubt he will be a great addition to our defence. He will bring experience, versatility and a great character to our playing group. We're looking forward to having Iain join us in April and welcoming home another talented South Australian to the Adelaide United Football Club."