Amstrad's head of legal, Richard Hastings, is to join Hammond Suddards' London office at the end of October and is taking a $200m lawsuit with him.
Hastings is organising Amstrad's on-going legal action against US computer components company Western Digital Corporation and is likely to be kept busy until the middle of next year.
Amstrad is suing Western Digital over the quality of the hard disk drives it supplied to the company during its failed foray into business computers in 1989.
The trial is taking place in Los Angeles.
In November last year, Amstrad settled a separate court action when American disk drive manufacturer Seagate Technologies agreed to pay it #86m.
Hastings was brought in by Amstrad four years ago with a brief to handle the company's litigation. He moved from Lincoln's Inn-based firm Tucker Turner Kingsley Wood & Co.
He said: "Once these actions are over, the company will not have another case like this. I have gone as far as I can with Amstrad."
He added: "Hammond Suddards is the right size, it is ambitious and it has an absolutely excellent intellectual property department."
Hastings becomes a senior associate in Hammonds Suddards' IP department and, as well as handling the Western Digital litigation, will continue to advise Amstrad on its digital media work.
A "delighted" Michael Mahony, partner in the IP department at Hammond Suddards, said: "Part of Richard's attraction is that lawyers that spend time in-house often have a deeper understanding of clients' business needs and demands."
A spokesman for Amstrad said that the company would announce its replacement for Richards in November.