The Glasgow-based engineering group said Mr Berry will become a non-executive director from March 1.
The 60-year-old will become a member of both the audit and remuneration committees.
Lord Smith of Kelvin, chairman of Weir Group, said: "Charles brings great experience of the industry and we are looking forward to benefiting from his contribution in the future."
Mr Berry was an executive director of ScottishPower plc from 1999 to 2005, latterly as chief executive of the giant utility's UK operations.
He was removed from the board along with former finance director David Nish by then chief executive Ian Russell hours before E.ON announced it was considering a cash bid for the company in September 2005. E.ON abandoned a takeover bid pitched at £10.7 billion two months later.
Mr Russell was replaced by Philp Bowman in January 2006.
ScottishPower succumbed to a £12bn bid from Iberdrola in November 2006.
Mr Berry joined the board of Drax Group, which runs the giant eponymous power station in North Yorkshire, in December 2005. He has chaired the company since April 2008.
Mr Nish became finance director of Standard Life in 2006. He has been chief executive since January 2010.