Sir Kyffin was a supporter of the project to house his works on Anglesey

The target was reached after the Welsh Arts Council agreed to contribute �250,000.

Construction of the Oriel Kyffin Williams will begin later this month.

Sir Kyffin, who was widely regarded as the leading Welsh artist of his generation, died of cancer last September at the age of 88.

There were immediate calls for a permanent memorial to the artist, known for his stark oils portraying his native north Wales.

Wales' richest artist Andrew Vicari said the memorial should be in Cardiff , but Anglesey's political leaders argued that it should be on the island which Sir Kyffin loved so much.

Rocks at Glyderfach was sold at auction last month for �30,000

The assembly government also supported the Anglesey project and it was decided that the gallery would be set up at Oriel Ynys Mon at Llangefni, which did not have enough room to display all his work.

Sir Kyffin, who was a member of the Royal Academy, was himself an enthusiastic supporter of the project having donated more than 400 works to the gallery.

On Thursday, Isle of Anglesey leader Gareth Winston Roberts said: "I am glad to be able to announce that the construction of Oriel Kyffin Williams will begin this month.

"The authority has made a substantial investment in order to make this scheme a reality, as well as succeeding in drawing additional funding and support from a number of our partners, including the Arts Council of Wales and the Welsh Assembly Government."

Since his death, interest in Sir Kyffin's work has increased and last month two of his oils sold for more than �30,000 each at an auction in Bath.

The sale also included items from Sir Kyffin's Anglesey home, such as a red easy chair he often sat in when visitors called. It sold for �80.

The gallery to Sir Kyffin, built in the courtyard of the neighbouring gallery, is expected to open on 1 March 2008.