The Sharks utility back, who won a World Cup winners medal while still only 20, told the French sports newspaper L'Equipe that he was moving to get out of the limelight in his home country.
Racing Metro have risen to the top rank in French rugby after winning ProD2 last season nd Steyn will get to work with former All Blacks outside half Andrew Mehrtens in the French capital.
Steyn has become one of the pin-up boys of South African rugby since winning a World Cup winners medal in Paris and he played in four different positions in 10 of the Springboks' 13 tests in 2008.
"I always told myself that I'd come to play in France," Steyn told L'Equipe
Exactly when he will join his new club is still under negotiation. Racing Metro want him to link up with them after the series against the British & Irish Lions, but the likelihood is that he will play out the Tri Nations and, possibly, the Currie Cup with reigning champions The Sharks.
"He is certainly not turning his back on SA rugby. Another reason is that he is very young and has a long career ahead of him," explained Steyn's agent, Gerrie Swart.
"Andrews Mehrtens will also be there and he is a good teacher for any guy who wants to play for a long time."
Swart also pointed to the pressure which Steyn had come under since making his Springbok debut in 2006 while still a teenager.
"You don't realise what kind of pressure there is on a guy who was 19 and won his first World Cup with South Africa - on the field and especially off of the field. In France he will have an opportunity to be just another player," added Swart.
"We don't yet know when his contract will start. It has to be cleared with the Sharks and SA Rugby, but he is contracted to the Sharks until after the Currie Cup series and the move can't therefore be earlier than November 1."