The contract will keep the 24 year old in Adelaide until the end of the 2012/13 season, and in the process see him become one of the longest standing servants of the club.

Despite being born in England, Cornthwaite has lived in Adelaide since he was young and is delighted to extend his stay with the Reds.

"I'm an Adelaide boy so there's no other team I want to play for, and I'm really happy to be staying at Adelaide United," Cornthwaite said.

"As soon as I heard that the club wanted to re-sign me, I was really happy and we went through the negotiations, which went really smoothly, so I'm very happy to be staying here."

Now in his fifth season at the club with 69 Hyundai A-League appearances to his name and two games shy of making his 100th appearance for Adelaide United in all competitions, Cornthwaite's new three year deal will make him an eight year player at the club.

"Obviously Viddie and the club have shown a lot of faith in me giving me a three year deal," he said. "I think over the five seasons that I've been here I have proven that I have improved each year and have been willing to learn and become a better player."

"I'm always going to make mistakes but as long as I limit those and learn from them, in three years time hopefully I'll be a very strong leader at the club."

Reds captain Travis Dodd and midfielder Lucas Pantelis are the only other two players still at the club from the first season of the A-League, and Cornthwaite is proud to become part of the Adelaide United landscape.

"It's a bit of an honour for me to still be here as one of only three players still here from the first season, and by the time this contract expires, I would have been here for eight years so it's a pretty big honour," the defender said.

"Not a lot of players in the A-League have stuck around at one club as long as me so I'm really proud of my achievement.

"To play at one club for your whole career would be something special and this is a club that I love and is close to my heart, so it would be an honour to stay here for as long as possible."

Arguably his greatest moment came during the AFC Champions League knockout stage last year. After conceding an own goal against powerhouse Japanese club Kashima, Cornthwaite turned from villain to hero as he scored a goal in the second leg to help Adelaide through to the semi-finals.

With that illusive championship still missing from United's trophy cabinet, Cornthwaite hopes he can help bring the prize to Adelaide in the near distant future and share in further success at the Reds in years to come.

"I'm still relatively young and inexperienced for a centre half so my best years are definitely still to come, there is still a lot of improvement I need to make in my game and with the help of Viddie (Aurelio Vidmar) and Phil (Stubbins) and the other coaching staff, I'm sure I can become a much better player than I am now," Cornthwaite added.

 "The club has had a lot of success without winning a championship so that's something all of the players at the club are striving towards."

 While he has a championship firmly in his sights, Cornthwaite's most immediate focus is on Saturday night's clash against Central Coast Mariners at Canberra Stadium. Kick-Off is at 7.00pm AEDT (6.30pm ACDT).