Emmerson, who has practised at Freshfields for 11 years, will become Milbank's first UK-qualified corporate partner in London when he joins the firm in April.
The announcement marks the first time in five years that a US firm has scored a high-ranking, magic circle corporate partner. Mike Francies was the last to defect when he left Clifford Chance for Weil Gotshal & Manges in 1998.
Emmerson is only the second Freshfields London partner to opt for a US firm, after James Starkey, a structured finance expert, moved to Cadwalader Wickersham & Taft in 1997.
During his time at Freshfields, Emmerson has cultivated a strong reputation, notably in equity capital markets.
Milbank's corporate department in London is currently staffed by US partners Michael Goroff and Crayton Bell, the latter having relocated from New York last July.
The firm's most high-profile deals in the past year have involved working for Goldman Sachs Capital Partners, including the E2.7bn (£1.84bn) leveraged buyout (LBO) of industrial gas group Messer Griesheim.
As counsel to Goldman Sachs, Milbank has also worked very closely with Freshfields on two other high profile deals – the €2.5bn (£1.7bn) LBO of Cognis, where the buyers were Goldman Sachs and Schroder Ventures, and this year's purchase of Deutsche Telekom's remaining cable business.
Emmerson told The Lawyer: “Milbank is a high quality and likeable group of people – rather like Freshfields. However, in Europe, its M&A business is, obviously, of different scale and focus. Developing new opportunities has always been one of the most enjoyable aspects of the job for me and I'll be able to do more of that across a number of European jurisdictions.”
A Freshfields spokesperson said: “We are sorry to see him go, but we understand his reasons.”