Bryan Cave has chosen Therese Pritchard as the first chairwoman and the first leader from outside its St. Louis base in its 140-year history, as the firm, which has a sizeable Atlanta office, adapts to the 21st century.

Pritchard, who leads the white collar and securities enforcement practice from Washington, was elected Bryan Cave’s next leader by the partnership on Monday. She will step into the role on Oct. 1, working as chair-elect with the current chairman, Don Lents, for the transition period, the firm announced Wednesday.