Adrian Phillips joined Garretts nearly six years ago and played a key role in building the Reading office into a seven-partner practice with 35 fee earners serving the Thames Valley market.
His departure is the latest in a string of high-profile defections from the firm's regional offices in the past year.
Garretts has, however, strengthen its City practice with this week's hiring of banking partner, Douglas Colliver from the London office of US firm, Dewey Ballantine.
Commenting on his departure, Phillips, says: "I have always wanted to run my own firm and now feels like the right time to fulfil that ambition." Peter Ridley, Garretts' managing director says: "Adrian has made an excellent contribution to Garretts and we are sorry to see him go. He leaves with our very best wishes for the future.