He was born in Kapilavatthu as the son of Suddhodana's chaplain. He received faith on the occasion of the Buddha's visit to his own people, and entered the Order. Overmastered by corrupt habits of mind and character, for twenty five years he was unable to develop concentration. This so distressed him that he was about to commit suicide, when, inward vision suddenly expanding, he attained arahantship (Thag. vs. 405 10. ThagA.i.448f). According to the Dhammapada Commentary (DhA.ii.256f), he tried to kill himself by making a snake, caught by the monks, bite him. But the snake refused to bite, in spite of all efforts to provoke him. Sappadāsa then threw it away, thinking it to be non poisonous. But the other monks declared it was a cobra, because they had seen its hood and heard its hissing.
Sappadāsa acted as barber to the monastery, and, one day, taking a razor, he applied it to his windpipe as he leaned against a tree. And then he thought how blameless his life had been and was filled with joy. Thereupon he developed insight and became an arahant. When the monks reported this to the Buddha, the Buddha said that the snake had been the Elder's slave in his third previous life, and therefore did not dare bite him. This incident gave the monk his name, Sappadāsa.