The reshuffle follows the departure of chief executive Manny Roman in July, who left to join PIMCO.
Rattray will be responsible for Man GLG, Man AHL, Man Numeric, and Man Solutions.
This was previously part of recently installed CEO Luke Ellis' role while he served as president of the firm. Rattray will remain CEO of Man AHL and will continue to lead the business strategy.
Man Group also intends to appoint Mark Jones, currently co-CEO of Man GLG, as chief financial officer and as an executive director of Man Group.
President of Man Group Jonathan Sorrell's role has developed to include a number of areas across the business and the intention is that he will step down as CFO, following an orderly transition to the new CFO.
Another change is the appointment of Robyn Grew to the newly-created position of chief administrative officer of Man Group. She will have responsibility for the firm's infrastructure, operations, technology, compliance, legal, human resources and facilities functions. Grew was previously Man Group's general counsel and global head of legal and compliance.