Ajahn Funn Ācāro was born in 1899 in Phannana Nikhom district, Sakon Nakhorn province, in northeastern Thailand. In 1919 he was ordained as a monk in a village monastery near home, and the following year he met Ajahn Mun, one of the founders of the Thai Forest Tradition.
In 1925, when he was sure that he would be able to give his life to the practice, he reordained in the Dhammayut sect, and then went to live with Ajahn Mun for his first Rains retreat. For the next 40 years, he wandered throughout northeastern Thailand, facing and overcoming many hardships — wild animals, lack of food, and recurring diseases. Because of his kindness and strength of character, he soon developed a following, both lay and ordained.