The hedge fund said it has entered an irrevocable, non-discretionary arrangement with Merrill Lynch International to repurchase ordinary shares in the company, up to a maximum consideration of $100m during the period from today up to and including 19 October 2017.
"The purpose of the programme is to return surplus capital to shareholders," the group said.
Man Group is repurchasing around 66m shares, based on the current share price and sterling to dollar exchange rate.
The firm said the buyback is in line with its policy to "distribute available capital surpluses to shareholders over time, by way of higher dividend payments and/or share repurchases, while maintaining a prudent balance sheet".
Man Group recently announced that it was launching a new global private markets business, having bought property manager Aalto.