The 32 year-old suffered an incapacitating knee injury which prevents him from training and from playing professional rugby.
Evans made 33 appearances for Wales and was selected for the British & Irish Lions tour to Australia in 2013.
The lock made 129 appearances for Ospreys, before joining Bristol in 2014, where he made 29 appearances.
“I’m deeply saddened to end my professional career now, however, the knee injury I suffered whilst playing for Bristol prevents me from achieving full fitness and will permanently affect my capability to perform,” Evans told bristolrugby.co.uk.
“While I’m sad that my playing career has come to an end, I’m looking forward to the next chapter and exploring new opportunities.
“I’ve been fortunate enough to have an incredible career and I’m honoured to have had the opportunity to represent my country, winning successive Six Nations titles.
“I’m grateful to the Ospreys and Bristol – two fantastic clubs where I have met great people and hold fond memories.
Head Coach Mark Tainton added: “We thank Ian and wish him the best of luck for the future.
“Ian helped Bristol to promotion in 2016 and has been an excellent ambassador for the Club. He’s suffered a challenging period here with his knee injuries and, ultimately, Ian hasn’t been able to play a regular run of games. We are grateful for his contribution – on and off the field.”
