The 33-year-old tighthead played for his local club Gala then joined pro side Borders Reivers in 2003 before going on to have stints with Edinburgh, Glasgow and finally London Irish.
He made his international debut during the 2009 RBS Six Nations against Wales and went on to win 40 caps for Scotland, including two appearances at the 2011 World Cup in New Zealand.
The qualified doctor – who will return to medicine now that his playing days are over – said: “I have enjoyed my time at London Irish, but I feel the time is now right to move my attention towards returning to medicine which I intend to achieve by next summer.
“London Irish is a club steeped in history and tradition, and the foundations are very much in place for it to make an immediate return to the Aviva Premiership.
“Representing my country was the pinnacle of my career, and to have played 40 times for Scotland fills me with immense pride. I feel very privileged to have fulfilled a lifetime ambition and to have made memories which will last a lifetime. I’m now however focused on the next chapter, one that I’m very much looking forward to.”
Head of rugby operations at London Irish, Glenn Delaney said: “Geoff has had a fabulous playing career that has seen him play at the very highest level for Scotland, and he has been a great professional to have at London Irish both on and off the field.
“I speak on behalf of everyone connected to the Club in wishing Geoff and his family all the very best for the future.”