Over the Christmas period, M&S attracted more than 9 million visitors to its online store and sales rose 70 per cent. In January, the retailer announced that it would relaunch the site before Easter to try to capitalise on its popularity.
Key changes include more ways to search for merchandise, real-time availability of products and a 'What's hot' area that will highlight seasonal fashion trends.
An M&S spokeswoman said: 'The web site has changed quite considerably - the look and feel of it is totally different.
'The limitations of the old site, in terms of customers being able to track orders, were beginning to be exposed. Using Amazon's expertise, we have been able to make the search and tracking options much more specific,' she added.
Customers will be able to buy from M&S's entire range of 30,000 items - more than is available in any high street store.
Retail technology specialist Conchango helped M&S with the integration and development of the site.