"I have been thinking about it for a while and decided it's a good time for me to go," the popular Glasgow full back said.
"It's been a bit of a fairytale really, two World Cups, 40 caps and a Five Nations Championship win, but I didn't think I would be heavily involved longer term under (new coach) Matt Williams, because he has to be looking towards developing a new squad and I won't be around for the next World Cup.
"I've got a year left on my Glasgow contract so this gives me a chance to look at the mentoring and analysis side, helping our coaches," he explained. "There will be options when I finish playing, but the opportunities are greater for me in Scotland and I'm desperate to still play for Glasgow.
"Having been involved with them throughout I feel we have really under-achieved. We've played some great rugby, but consistency has been our biggest problem. However, looking at the young squad we've got there is great potential and the work ethic is excellent."