Top trial attorney Joan Lukey is leaving Ropes & Gray a year ahead of hitting the firm’s mandatory retirement age to join the much smaller Boston-based firm of Choate, Hall & Stewart, where she will be a partner and chairwoman of its complex trial and appellate litigation group.

Lukey, who turns 65 at the end of the year, says she would have had to retire from Ropes & Gray in December 2015 as per the firm’s policy, one of the main reasons why she decided to make the leap to Choate Hall.