The Aussie international won the award after polling the most votes cast by Oceania's national federations and pipped Middlesbrough's Mark Schwarzer and Parma's Marco Bresciano to the title.
"Tim has had a wonderful season and is a deserved winner of the OFC player of the year award," said OFC General Secretary Tai Nicholas.
"He is unique in that he has played for two Oceania nations, Western Samoa and Australia at various levels.
"It was a fabulous year for Tim scoring the winner in an FA Cup semi-final which has catapulted his career to the next level.
"He has certainly served as a fantastic role model not just for youngsters in Australia but also in Samoa."
Cahill left The Den last summer in a controversial £1.5 million move to Everton shortly after winning the first of his seven caps for Australia, making his last appearance for The Lions in the FA Cup Final against Manchester United.