The final price was undisclosed, but the 49-bedroom hotel was marketed by Christie + Co at a guide price of £2.6m.
The Clubhouse Group already owns the Mercure Abbey Hills Hotel, also in Milton Keynes, as well as several European hotels under management.
Located within a Georgian property, Mercure Parkside House is also a wedding and function venue, and has five conference rooms.
Stewart Harkness, associate director at Christie + Co, said: “This opportunity came about at the perfect time for The Clubhouse Group, following the huge success in revamping the Mercure Abbey Hill Hotel, which we sold to Nazim in 2012.”