The Cardiff Blues hooker returned to action in the New Year after recovering from ACL surgery and is fit and available for the remainder of the season.
But he will call it quits in May and is determined to go out on a high by helping secure Heineken Champions Cup rugby once more for his home region.
Rees, 38, said: “I’ve made my decision to retire based on a few reasons but mainly age isn’t on my side anymore and it’s been a tough journey with an injury like an ACL reconstruction and its rehabilitation. I’ve managed to get through that and I’m now able retire on my own terms after an illustrious career.
“I haven’t featured much this season because of the injury but now I want to go out on a high. We have three months left and hopefully I can play a part in those remaining games.
“The next few weeks are going to be huge, especially when you consider how tight it is in the league table.
“We’ve put ourselves in a decent position in the PRO14 and we have some big games coming up. We’ve had a taste of the Champions Cup again and that’s where this region wants to be and where the players want to challenge themselves.”
Rees has already played more professional games of rugby than any other Welshman with 329 professional club and regional appearances to his name as well as 60 Tests for Wales and three for the British & Irish Lions.
His achievements are made all the more remarkable given the fact that he was diagnosed with testicular cancer in 2013, something in which he overcame to continue playing.
He continued: “Starting out at Pontypridd in 2000, I could never have imagined I would achieve what I have. It’s amazing just to be playing professional rugby at the age of 38, especially in the front-row and to have played almost 400 games takes some doing.
“I’ve been very fortunate and I’m really proud of everything I’ve achieved. Playing for Wales is every kid’s dream and the Lions is a big one, especially playing in Test matches. To have also captained the Scarlets, Wales and Cardiff Blues is a massive honour and something I will cherish for the rest of my life.
“The only real frustration is being named captain for the 2011 World Cup and then being ruled out through injury. I would really have liked to have played a part in that, knowing how well we had prepared.
“Being diagnosed with cancer were some of the real dark days of my career. I did think that my professional playing days were over.
“Looking back, I probably came back a bit too early but the icing on the cake was earning selection on the Wales tour to South Africa in 2014 and winning two more caps. Overcoming cancer to play a few more seasons is more than I could have imagined.”
Rees is now considering his next steps and would ideally like to remain within rugby. Cardiff Blues head coach John Mulvihill has led the tributes to the man known as Smiler and believes he still has a huge amount to offer to the game.
Mulvihill said: “Smiler is a real warrior of the game and his body and mind have played a massive part in Welsh rugby over more than a decade of service. He is a true champion who has beaten challenges both on and off the field during his illustrious career.
“I spoke to Smiler after his initial injury at the end of last season and said it was his call on whether he was willing to put his body through a lengthy rehab to try and get back to being the number one hooker at the club. I never doubted he would make it back and it was great to have him lead the team out in our final Heineken Champions Cup game in Glasgow last month.
“It was always my intention to let someone who has given such great service to his club and country over so many years to go out on his terms. He is someone who doesn’t want to hang on to make up the numbers, he will go out on his terms and with plenty to look back on with pride.”
“Our entire squad, staff and the Cardiff Blues and Welsh rugby family wish him and his family all the very best for the future. I’m sure he will continue his passion of rugby on in some capacity and share his wealth of knowledge with both current and future players both at the Cardiff Blues and within our region.”