Sydney partners Jenne Tzavaras, Joanna Apostolopoulos, and Ivan Medak are bringing 20 other lawyers with them.
Employment law specialist Tim Lange was a partner at Hunt & Hunt.
Damian McNair, former head of DLA Piper's Asia Pacific projects and finance team, is joining Tony Holland, the firm's former Australia chairman, at Gilbert + Tobin.
Adrian Tan is joining the Singapore firm as a director from Drew & Napier.
Michael Perez is expected to join the firm in January from Allens.
Tony Holland is also DLA Piper's Asia Pacific finance head and previously served as chief executive officer of the former DLA Phillips Fox.
Anthony Root is now a senior advisor in the Hong Kong office of Moelis & Co.
M&A specialist Jeremy White was previously a counsel at Allen & Overy.
Former Hogan Lovells partner Gabriela Kennedy will also head Mayer Brown JSM's regional technology, media, and telecommunications practice.
The shifting market, a series of departures and leadership changes—in the U.S. as well as Asia—have raised questions about the firm's Asia strategy. But chairman Bradley Butwin insists that O'Melveny's commitment to Asia is as strong as it ever was.