Music law specialist Jay Quatrini represents mostly "urban" clients - rap, hip-hop and reggae artists - from both sides of the Atlantic.
He spends alternate fortnights in New York and London and will continue this arrangement at Davenport Lyons.
The firm's New York base will be in the offices of a 20-lawyer entertainment firm.
Quatrini explains: "We're going to be in the same suite and they can provide additional resources if needed. For example, I don't really do trademark work, but there's a guy there who does, so I can ask him to look at it."
James Ware, head of copyright, music and entertainment at Davenport Lyons, says his firm has many informal links with US firms which will continue.
"We will have offices within another firm but there is no formal association," he says. "We do not see this as interfering with our relationship with the many firms that we deal with in the States. We are not setting ourselves up in competition."
A partner at Mishcons for three years, Quatrini has previously worked at New York-based Mudge Rose Guthrie Alexander & Ferdon (former-president Richard Nixon's old firm) and sports lawyer/agent, Bob Woolf.
Quatrini says he joined a UK firm because "the flight between New York and London isn't too bad" and he wants to do different deals.
Of his move to Davenport Lyons, he says: "The emphasis they have on entertainment and media is more directly relevant to what I do and they are eager to embrace a New York and American practice."
Ware says: "Jay is a very special operator, being based partly in the UK and partly in the US.
"He's going to bring an extra dimension to our practice. He represents a lot of grass-roots artists and new talent whereas a lot of our clients are more established artists and large corporations."
Mishcon's corporate head Larry Nathan says: "We wish him the best.
"I suspect he left because his practice was mostly New York-based. We wanted him to integrate into our UK media practice, focusing on converging technology.
"We have no music practice. We had one when Jay joined, but it dates back to a previous time in the firm's history."