The hooker, who finished last season with Northampton Saints and had been due to join Gloucester Rugby later in the summer, has been advised to retire on medical advice due to the effects of a degenerative neck injury.
The 34-year-old, who was capped twice by England, made his 200th Aviva Premiership Rugby appearance in the final match of the 2011/12 regular season, with his 201st, and final, match coming in the semi-final loss to Harlequins.
Long played 38 times in all for the Saints in his two-and-a-half years at the club and picked up an LV= Cup winners' medal in 2010. His career also included spells at Bath, Munster, Rotherham, Newcastle Falcons and Cetransa El Salvador.
Although disappointed that he could not continue his career, Long says that he had no regrets after playing rugby for nearly 30 years.
"I've achieved everything I wanted to achieve out of rugby," he said. "I started playing aged four and went all the way to the top to play for England at Twickenham. I've had 200 games of Premiership Rugby and played for some great clubs who have all had magnificent supporters, and I'm at peace with the fact I'm having to retire.
"That said, I had signed for Gloucester so I wanted my career to continue, but I'd been carrying an injury which was causing me a few problems towards the end of last season, and the rehabilitation time from an operation would have meant that I would have been on the sidelines well into next season, too.
"I am devastated that I was not able to contribute to Gloucester in the way that I hoped as I was really excited about playing for such a great club, but am nevertheless glad that my career finished in the way that it did, playing for a great club like Northampton in the Aviva Premiership Rugby knockouts. I've loved being at the Saints and I'm very happy I was able to contribute to the first team in a meaningful way, especially over the past few months.
"It was also amazing to have my sons with me on the field after the Worcester game at Franklin's Gardens, and to have the support of my family has been a big inspiration.
"I have had an awesome time playing for some great coaches and alongside some world-class players and I've learned something from every club I have been at. I would especially like to thank Bournemouth RFC, where I started, and if it hadn't have been for them I wouldn't have had the life and career which I've had."