The firm has added four lawyers, including three senior lateral Hungarian appointments. The expansion coincides with Jonathan Porteus and Eva Hegedus' promotions to partner level.
The growth means A&O now has two partners and 10 lawyers in Budapest. Porteus says he and co-head Hegedus aim to expand to 15 lawyers.
Porteus says: "Clifford Chance and Camerons are both bigger than us, but we've reached critical mass and with our size now, we are big enough to compete with anyone."
The most senior appointment is Peter Danko, who joins from investment bank ING, where he was head of legal in Budapest. He will head A&O's Hungarian banking practice.
Banking lawyer Tibor Nagy also arrives from ING. Richard Eordogh joins from Hungarian firm Strook & Strook & Lavan. Alex Cook, a corporate and international equities lawyer, has moved to Budapest from the firm's London office.
The office is growing after the end of A&O's wrangle with the Hungarian authorities over the Hungarian government's regulations requiring all foreign firms to form an association with a local firm.
But Hegedus has formed her own local firm, with which A&O is technically associated, now making A&O's Hungarian office Eva Hegedus Ugyvedi Iroda in association with A&O.