The new deal will see him stay in the Sydney defence for a further season.
The 30-year-old has been struggling with a knee injury and has been out of action for a month, but returned against Perth last weekend.
“I am really enjoying playing for Sydney FC. The club has been fantastic to me and we have a great squad that is really motivated to play top football. I am delighted to be given the opportunity to extend my time in Sydney.” Keller said.
“I love the Sydney lifestyle on the Northern Beaches and look forward to getting to know the city better this summer.”
