The retailer said that the move will allow customers to enable search, browsing and to make purchases easily from any web-enabled mobile device.
The site will be in sync with the main M&S website so that customers can log into their web-account to manage shopping baskets from their mobile. There will be no need for customers to download an app or any software.
Customers will have access to more than 24,000 products, including clothing, home and furniture, technology, gifting as well as the majority of functionality from the main M&S website.
It does not however include M&S general food offering.
The site was developed by Usablenet, a New York based consultancy, with the design work was carried out by London-based MIG (Mobile Interactive Group).
In the first three months of 2010 M&S witnessed sales at online shopping division M&S Direct grow 48% having seen a 32% rise in the three months to Christmas.
This benefited from the re-launch of the website in October, adding new products, new services and also international delivery.
It also improved usability of the site last year which resulted in the site topping the Webcredible poll of the best online high street retailers in the UK.
Dave Hughes, director of M&S Direct, said: "This is a major step forward in mobile retailing. Mobile optimised shopping sites have been done before by specialist retailers, but M&S entering the market with 21 million customers, one of the UK's most recognised brands and a well-known range of products changes the mobile retail landscape."
He added: "Even before the site has launched, hundreds of thousands of customers are already shopping with us on their mobile phones and market data is telling us that this will soon be millions. The new site allows these customers to browse and buy from their mobile device without the frustrations that come with trying to do the same on a traditional website."