The 130-year old group, which has reported 10 straight quarters of declining underlying sales in its general merchandise division including clothing, said on Tuesday its new site had gone live after over three years of development.
It replaced a previous platform provided by Amazon since 2007.
"We want to own our car, not rent it," Laura Wade-Gery, the former Tesco executive recruited by Chief Executive Marc Bolland to develop M&S's online capability, told reporters.
Bolland has high hopes for the new site, seeing it as crucial to his initial 2.3 billion pounds three-year drive to transform M&S into an international, "multi-channel" retailer, connecting with customers through stores, the Internet and mobile devices.
The new site will complement M&S huge e-commerce distribution centre at Castle Donington in central England that opened in May 2013 and is building capacity for the peak trading season at Christmas 2014.
Wade-Gery said the new site provides customers with a better browsing experience and an improved buying process.
"Buying a photo"
New features include product images that are up to 50 percent bigger than on M&S's previous site, available as either cut outs or on a model shots, as well as zoom features, catwalk and 360 degree video.
"If you are shopping online, you are essentially buying a photo," said Wade-Gery.
The new site also includes an editorial hub, with M&S aiming to capitalise on research showing that shoppers who engage with editorial content were 24 percent more likely to buy.
The first phase of the new website launch will focus on M&S's existing 6 million online customers. Improved delivery options will follow.
Wade-Gery said the future prize for M&S will be to engage the 14.5 million shoppers who currently visit the firm's stores but only shop online with competitors.
M&S shares, up 28 percent over the last year, were up 0.4 percent at 496 pence at 1612 GMT.
© Thomson Reuters 2014