Pietersen, who played 70 Tests for the Springboks between 2006 and 2016, has agreed a two-year deal with the French giants, joining them from English club Leicester Tigers.
Pietersen, who turns 31 in July, joined Leicester last year and made 14 starts and one appearance from the bench in the 2016/17 campaign, scoring three tries.
Pietersen took to Twitter when his new deal became official, saying he was looking forward to joining a club he always wanted to be part of:
He also thanked Leicester and their fans for their support:
Really excited to start my new chapter at @RCTofficiel a club I've always respected and wanted to be a part of ????— JP Pietersen (@jppietersen14) June 21, 2017
Thank you @LeicesterTigers for the season and especially to all the awesome Tigers fans for making me feel at home ??????— JP Pietersen (@jppietersen14) June 20, 2017