Sonberg will be replaced by a trio of current partners. Robert Grammig, co-leader of the firm's corporate, M&A and securities practice group, will serve as Holland & Knight's chair and CEO. Meanwhile, David Whitestone, executive partner at the firm's D.C. office, will serve as managing partner and Tiffani Lee, the firmwide diversity partner since 2008, will serve as deputy managing partner.

Sonberg led the Am Law 100 firm for 16 years, and recently steered the firm through two blockbuster mergers with Thompson & Knight and Waller Lansden Dortch & Davis with the help of Grammig. Overall, Sonberg's tenure saw the firm grow by almost 900 lawyers, 17 offices and close to $1 billion in revenue.