Scorer of a record 1,083 points for his country, almost twice as many as any other player, O'Gara famously kicked the drop goal that handed Ireland a first Grand Slam in 61 years in 2009.
The 36-year-old fly-half was a twice Heineken Cup winner with Munster, a competition in which he also holds the points record by a wide margin, and toured with the British and Irish Lions three times.
American-born O'Gara, whose boot was relied on so many times in an international career that spanned over a decade, struggled for form this season and was dropped from the Irish squad during this year's Six Nations championship.
His last act for his country in his 128th appearance against Scotland in February was a bizarre crossfield kick from inside his own third of the pitch that summed up Ireland's capitulation during the final days of coach Declan Kidney's reign.
However O'Gara, Munster's most decorated player, wound the clock back to give a stirring performance for his province in last month's Heineken Cup semi-final when they almost pulled off another remarkable, against-the-odds win over Clermont Auvergne.
Munster said O'Gara would take up his new role in France from next season. Racing recruit Sexton had a tense rivalry with O'Gara before prising the Irish number 10 shirt from him in recent seasons.
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- Heineken Cup