The South African first five-eighth has been signed on a four-year contract, with the club announcing the deal on Tuesday night.
Lambie, 26, who has 56 caps for the Springboks - the last being in November, 2016, has been able to secure an early release from his contract with the Sharks Super Rugby side and will join the French side from November 1, subject to passing a medical.
"This world-class flyhalf is signed as an 'additional player' and his signature completes the Racing recruitment campaign," the club said in a statement on their website.