Twickenham-based Real Ale has been supplying the multiple with bottle-conditioned ales from regional brewers for three years.
Managing director Nicholas Dolan said: “We work in conjunction with M&S to find regional breweries to represent their beers.
“We purchase the beers from brewers and have them labelled. All are brewed exclusively for M&S.”
The nine beers supplied include Scottish Cairngorm Ale, Yorkshire Bitter from Cropton brewery, Norfolk Bitter from Woodfordes Broadland brewery and Cornish IPA from St Austell brewery.
Real Ale is celebrating its birthday with a further boost to business after being appointed the Camra beer club which boasts around 1,000 members.
Dolan added: “Promoting small- and medium-sized breweries, in many cases from rural communities across the UK, is fundamental to our ethos.”
To mark its fifth birthday Real Ale is offering 10% off all purchases and five-for-four this weekend (14-16 May).