He belonged to a brahmin family of Benares and was expert in the Vedas. Later, owing to his association with Vimala Thera, he entered the Order and lived with him. (But according to ThagA.i.377, Vimala was ordained by Somamitta). But finding Vimala given to sloth and laziness, Somamitta left him and joined Mahā Kassapa, under whose direction he soon attained arahantship. Later he visited Vimala and rebuked him. Vimala then put forth effort and became an arahant.
Somamitta was a householder in the time of Sikhī Buddha, and, very pleased with the Buddha, he picked some kimsuka-flowers from a tree and offered them to him (Thag.vs.147f ; ThagA.i.267f).
He is perhaps identical with Kimsukapupphiya Thera of the Apadāna. Ap.ii.435; but see ThagA.i.87.