The 31-year-old front man, nicknamed Gucci, arrives from Cypriot side APOEL Nicosia and is in contention to make his Sky Blues debut as soon as this Sunday’s A-League clash with Melbourne City.
Ghoochannejhad has represented his country on 44 occasions, scoring 17 times in the process, and has been to two World Cups with Team Melli.
"I'm excited to be joining Sydney FC and looking forward to the challenge of the A-League and AFC Champions League," Ghoochannejhad said.
"To be joining Australia's most successful club is a fantastic move for me, and to test myself against the best in Australia and Asia will be a fantastic experience," he added.