The 33-year-old began his career with Toulouse in 2000-01 and went on to win four French league titles and the European Cup on three occasions.
After 15 years at Toulouse, Poitrenaud says it was appropriate that he should retire once the club decided against extending his stay.
"I wanted to stay another year but the club didn't want it," Poitrenaud told Boudu. "It was going to have to stop at one point or another.
"I've had bad luck with injury this last year. So this season, I've played less, I've had more trouble staying in rhythm.
"This is a situation that I had never known before. But deep down, whatever the moment, it is sad to leave your club."
Poitrenaud also won 47 caps with France, scoring seven tries and playing in the teams that reached World Cup semi-finals in 2003 and 2007.