The new deal that will keep him at the club until the end of 2018.
Gray was revealed by AFL.com.au in late October to be close to a new deal, thereby taking him off the 2015 free agency market.
The livewire midfielder, 26, had a career best season this year where he claimed his first John Cahill Medal as the Power's best and fairest, took out the Coaches Association Champion Player of the Year award and gained All Australian selection.
Gray booted 42 goals this year and amassed a competition-high 33 goal assists.
His new deal will see his stay at Alberton surpass 10 years.
"I think this will take me through until I'm about 30 and that will be 12 years at the footy club and [I] definitely see myself as a one-club player," Gray said.
"I've got some really good friends here and coaches as well and I'm really settled here in Adelaide.
"A few years there we weren't going so well so I've really enjoyed the last couple of years and playing some finals footy.
"I'm looking forward to doing some more of that in the future."
Port Adelaide coach Ken Hinkley had remained confident Gray would re-sign with the club, given the faith the Power showed in their All Australian by offering him a new deal in 2012, shortly after Gray had been through a knee reconstruction.
Gray's stunning comeback from that injury saw Hinkley laud him as the best player in the AFL, just after the club's 2014 season ended at the hands of Hawthorn.
“Robbie’s year really was outstanding and it really reflected the growth in the whole group of which he is clearly a vital member,” Hinkley said on Tuesday.
“He helped set the standard for the whole team and I’m looking forward to him continuing in the same vein this upcoming season.”
Gray too hoped he could take his game to a new level in 2015.
He said his experience of playing alongside fellow superstars during the recent International Rules Selection would help him improve both on and off the field.
"Some of the professionalism of some of them and the leadership – we had (Joel) Selwood, (Luke) Hodge, those sorts of guys, (Nick) Riewoldt, just really impressive leaders," he said.
"Leadership is probably an area I can improve in. I'm a pretty quiet sort of guy but those guys really do talk up and lead by example.
"I was really impressed by the leadership of those sorts of guys…things like recovery and diet - you just pick up on little things that they do."
