Ms Crosbie (pictured) currently leads Allens' competition practice and has been a partner of the firm for 15 years.
“I am delighted to serve as chairman and will play an active role in our relationships with clients, alumni, community partners and with the broader business community,” Ms Crosbie said.
“I look forward to working across the firm to guide the board as it provides counsel to the managing partner and executive committee and the partnership.”
Ms Crosbie will replace current chairman Ian Wallace, whose four-year term has come to an end.
Mr Wallace said Ms Crosbie is an outstanding partner and will play an important part in the governance, operational oversight and strategic initiatives of the firm.
“I am delighted to announce Fiona as the firm's next chairman. Fiona will bring to the position a love of the firm and a deep respect for its traditions, people and place in the market,” Mr Wallace said.
“Having served on the board, Fiona brings a strong commercial outlook and commitment to the firm's innovation and change agendas.”