The 32-year old has played 111 times for the Warriors in two spells with the club and has represented his country 25 times.
One of few players to have represented three Scottish professional teams during his career, Ryan played six times for the Borders and 14 times for Edinburgh before joining the Warriors.
After impressive displays in his first two seasons with Glasgow Ryan was named in the Scotland squad for the 2012 summer tour to Australia where he made his debut in a victory against the Wallabies.
A year later, Warren Gatland called him up to his British & Irish Lions squad following injury to Gethin Jenkins.
He played three times for the Lions and was named on the bench for the final test against Australia.
Ryan previously served with the Royal Signals and has also played for the Combined Services' under-21 team.
He scored the winning try for the Army in their 23-13 victory against the Royal Navy at Portsmouth in December 2005, a result that secured the Inter-Services Under-21 Championship for his team.
Away from rugby, Ryan owns and runs the Garden Shed Drinks Company with Warriors teammate Ruaridh Jackson.
Their bespoke gin is now on sale across Glasgow.
Speaking to Warriors TV, Ryan said: "Now is the right time to hang up my boots for both my body and my mind.
"The club has been a huge part of my life and a fantastic experience for me. I can attribute nearly everything in my life to this rugby club it will always mean an awful lot to me.
"There are so many games that stand out for me. Ulster back to back at home were two of the most physical games of my life and being part of a title winning season was pretty special.
"It was always an honour to represent my country too. My first cap, beating Australia in Australia was pretty special and any 6 Nations win was an amazing feeling.
"I am so embedded in this Glasgow Warriors, so is my family. I've invested so much of my time and my body in Glasgow that Ií'll always be a supporter."