The deal was signed after all regulatory authorisations and approval from competition authorities was given, enabling L'Oreal to buy the brand from current owner French retail giant PPR for an estimated €1.15bn.
The two companies first announced their intentions in January 2008, and the company was given the go ahead by the European Commission last month after fulfilling all the necessary competition requirements of the European Economic Zone.
YSL provides new building block As a part of L'Oreal's luxury division, YSL will now be under the responsibility of Marc Menesguen, who is currently president of the division.
Menesguen underlined the fact that the YSL brands had strong worldwide identities that were likely to 'compliment' the existing brands within the division, which already includes designer names such as Diesel, Ralph Lauren and Guy Laroche, together with other big names such as the Body Shop and Lancome.
The brands within L'Oreal's luxury division are focused on luxury cosmetics, and are particularly strong in make-up and fragrances - areas where YSL is already well established.
Increasing global reach "We are convinced that the support of our research and our strong international presence will enable them to increase their global reach," Menesguen said when discussing the future prospects of the YSL brand.
The transaction represents the enterprise value of YSL Beauté and will also include the Roger and Gallet subsidiary which makes perfumed soaps.
In addition, L'Oreal will have licenses for the fragrances and cosmetics of the Stella McCartney, Oscar de la Renta and Ermenegildo Zegna brands, although the former will remain the property of the PPR Group.
Although the Yves Saint Laurent and Boucheron brands will remain the property of the PPR Group, exclusive global long term licenses will be granted for their cosmetics and fragrance divisions.
PPR Chairman and CEO Francois-Henri Pinault said that L'Oreal would be able to offer a unique development platform for the brands and the agreement would allow YSL Beauté to take advantage of its "upside potential".