The distillery currently produces 5.7m litres a year. It will increase by 700,000 litres.
The extension will see two new 62,000 litre washbacks to add to the eight already on site. Further work will include a new mash tun and a new control system in the still house.
The work is scheduled to take six months, starting in June. The distillery will be closed to the public but the shop will remain open.
Diageo, which is the world’s largest drinks company and the largest scotch whisky producer, says the project forms part of its £600m rolling programme of capital investment across its Scottish sites.