Adofo-Mensah previously was the director of football research and development for the 49ers. He will work under new Browns general manager Andrew Berry, who was hired earlier this year.
The Browns have also hired former Indianapolis Colts general manager Ryan Grigson to their front office, with a title yet to be announced, according to a league source. Grigson, who was with the Browns as a personnel executive in 2017, worked as a consultant for the team leading up to the draft.
Adofo-Mensah and Grigson replace Eliot Wolf and Alonzo Highsmith, assistant general managers under John Dorsey, who was fired as Cleveland's GM in late December.
Like Berry, who graduated from Harvard, Adofo-Mensah holds an Ivy League degree from Princeton. He also earned his master's in economics from Stanford. Browns chief strategy officer Paul DePodesta (Harvard) and new coach Kevin Stefanski (Penn) also went to Ivy League schools.
ESPN's Seth Walder contributed to this report.