The London office of Sonnenschein Nath & Rosenthal scooped the work advising McDonald's – the US firm's existing client in the US – on its acquisition of the Aroma coffee chain for a reported £10m.
London office head Peter Borrowdale led a team of five on the deal, which included property partner Rupert Jones.
Finers, led by head of corporate and commercial Peter Jay, advised the shareholders of Aroma, while corporate partner Joanne Hamilton from SJ Berwin & Co advised Apax Partners, a shareholder and the original backer of the chain.
Sonnenscheins' UK office has previously done property work for McDonald's in the UK, while Eversheds and niche property firm Forsters have been used by the fast food chain on UK property deals.
But the deal is understood to mark the first time that McDonald's has outsourced significant corporate work in the UK – although Forsters has done some "small-scale" UK corporate work for the company.
McDonald's, which has more than 930 restaurants in the UK and annual sales exceeding £1.2bn, said the move would not distract the company from growth plans for its restaurant business.
Borrowdale, who joined Sonnenscheins from A&O, said the firm had won the work for "several reasons", including its relationship with McDonald's, but mainly because it had a "strong corporate team".