His son, Doytibet, announced the death of his father on his Facebook page and praised him for leaving behind the immortal work.
Mr Doytibet did not disclose the cause of the death but the Thai Rath Online reported that the artist died of hepatitis.
The religious ceremony will be held at Wat Depsirin.
Born in 1939 in Chiang Rai province, Thawan studied at the Poh Chang Arts and Crafts College and Silpakorn University.
His paintings are widely praised, both in Thailand and abroad, but it was in his home country where he found the widest appreciation. Art collectors and experts alike constantly seek his works.
He was announced a national artist in 2001. Thawan is survived by four sons.