Izzo’s deal means the young gloveman will stay with the Reds until at least the end of the Hyundai A-League 2019/20 season.
The 22-year-old started his professional career with Adelaide, serving as back up to Club Captain, Eugene Galekovic, and played seven matches in four years.
However, prior to the 2015/16 campaign, Izzo departed the South Australians and joined the Central Coast Mariners where he accumulated over 40 appearances.
Speaking on his three-year contract and returning home to Adelaide, Izzo said: “I’m so happy to be coming back to Adelaide because it’s every professional footballer’s dream to play in front of their family and friends regularly.”
“This is a fantastic opportunity for me to do that and when I left I always said that I’d love to come back one day.
“I honestly didn’t think it would be this quick, really only two seasons ago, but I’m glad this opportunity has come.
“Moving away and leaving home was tough, but I think it was probably the best move I’ve made in my young career so far.
“I was very grateful for the Club letting me go back then and I’m extremely grateful they’re taking me back now.”
Adelaide United General Manager of Football, Ante Kovacevic, was full of praise for Izzo upon his signing, saying: “We are very happy to have added Paul to our squad for the next three seasons.
“A couple of seasons ago, Paul made the decision to leave this Club to pursue more game time and to improve his abilities, which he has done.
“Despite being a young goalkeeper, Paul has shown his maturity and quality between the posts during his time at the Mariners and we’re sure he will only continue to improve.”