Dan spent seven seasons with Glasgow, scoring over 1000 points, and becoming a hugely popular figure with supporters.
He then spent two years at Cardiff Blues from 2010-2012 before ending his career at Connacht. Dan remains the PRO12's all-time leading points scorer.
He won 67 Scotland caps, scoring 266 points, including a Scottish record 17 drop-goals.
"I feel incredibly fortunate to have been able to play a sport which I love for over 11 years as a pro. My time in Scotland, Wales and Ireland has been the best years of my life, and I would like to thank all those who have contributed and helped me along this amazing journey," said Dan.
"Of course, my highlight was being able to wear the blue of Scotland, and something I will forever treasure and hold very close to my heart.
"I plan to stay closely involved with the game, through TV, commercial work and coaching, and I am really excited about the future and continuing to be involved in the sport I am so passionate about and that has given me so much."