The young midfielder has gone from talented prospect to crucial squad member in four seasons since arriving from Perth in 2015, and has been rewarded for his efforts with a new two-year deal which ties him down to Sydney until 2021.
O'Neill's impressive form, which has helped propel Sydney to two A-League Premierships, a Championship and an FFA Cup, has not been ignored with clubs in England, Holland and Switzerland all looking to sign the 24-year-old.
While happy to commit to Sydney for the next two years, O'Neill revealed he could have very easily made a move to the Championship with Aston Villa, one of a number of clubs in England's second tier making serious offers to secure his signature.
He admitted it was a big decision to turn down a move to England but felt his call to stay with the Sky Blues is the best one for his long-term career.
“I’ve had a fantastic four seasons already at Sydney FC and can’t see myself at any other club right now,” O’Neill said.
"There was interest in the last transfer window and previously but their was no defining factor for me to jump at something,
"It is my ambition to still play at the highest level possible, whether that be in Asia or in Europe.
"Sydney FC want to do everything in their power to make that a reality for me and it played a big part in my decision to stay."
One of O'Neill's main priorities is one day earning an international call-up, and he is confident he can follow the path paved by other A-League stars to earn a national team spot without making the move abroad.
"Rhyan Grant and Josh Risdon as well as a number of other A-League players are proof you can play in this competition and at a higher level," he said.
"One day I would love to say that I play for Sydney FC and be in an international team.
"It would be a very proud moment to do that here because coming from Perth as a relative unknown... Sydney FC have helped me through so much."
O'Neill has featured in all 17 of Sydney's A-League games this season, creating four assists and scoring one goal.
It's the second key resigning for the Sky Blues in as many days, after Grant signed a three-year extension on Wednesday.
Sydney FC's next game is away to Brisbane Roar on Friday night.
