The investment company, which was formed out of the merger of Standard Life and Aberdeen Asset Management last August, on Tuesday said Flint would be appointed non-executive director and chairman-designate on November 1, 2018, before taking over from Grimstone, who will step down on January 1, 2019, after 11 years as chairman.
"We undertook a rigorous and comprehensive international search to identify Sir Gerry's successor and we are very pleased that Sir Douglas will join the board and become its chairman,” Simon Troughton and Melanie Gee, co-chairs of the appointments committee said in a statement.
"His passion for our company, his strong track record as chairman and his international experience make him an ideal candidate to lead the board as we continue to build our global investment business,” they added.
Following this appointment, the company said its board would be made up of four executive directors, ten non-executive directors and the chairman - three women and 12 men.
Standard Life Aberdeen recently reported lower first-half profits and assets under management and administration, blaming challenging market conditions.
Shares in the company, which have almost halved in value during 2018, were 0.26% down at 265.55p in early afternoon trade.