He belonged to a brahmin family of Bārāṇasī and was expert in the Vedas. Later, owing to his association with Vimala Thera, he entered the Order and lived with him. (However, according to ThagA.i.377, Vimala was ordained by Somamitta). However, 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.147 f; ThagA.i.267 f).

He is perhaps identical with Kiṃsukapūjaka Thera of the Apadāna. Ap.ii.435; but see ThagA.i.87.