The gallery, celebrating its centenary year, has been awarded the Heritage Lottery Fund grant so it can 'restore and reveal a rich vein of hidden heritage'.
The creating connections project will see the Cooper transformed by an extension to create additional gallery space.
That extension will be built at the back of the building and will not involve moving the popular cafe.
That extra gallery space will allow a far larger proportion of the gallery's collection of 18th, 19th, and 20th century paintings to be shown – at present only five per cent can be displayed at any one time.
Coun Roy Miller, cabinet spokesman, said: "This is great news, the Cooper has been enriching Barnsley's cultural life for 100 years and now this funding means it can widen its offer, allowing access to all the works of art in its collection."
** The full story appears in the Barnsley Chronicle, dated October 3. **