A mahāsāla brahmin, ranking with eminent brahmins such as Caṅkī, Tārukkha, Pokkharasāti, and Todeyya (SN. p.115). He is mentioned as staying in Icchānaṅgala (M.ii.196), where he evidently took part in the periodical gatherings of brahmin leaders — and also at Manasākata (D.i.235). He was a follower of the Buddha, of whom he was a great admirer. He appears to have been in the habit of talking to well-known teachers of other schools and hearing their opinion of the Buddha, either for the purpose of comparing his own faith in him or of discovering their views. Two such conversations are recorded — one with Subha Todeyyaputta (M.ii.209), the other with Pilotika (M.i.175 ﬀ). His discussion with Pilotika he reported to the Buddha, who expanded it to form the Cūḷahatthipadopama Sutta. The Buddha also taught Jāṇussoṇi the Bhayabherava Sutta (M.i.16 ﬀ).
Jāṇussoṇi's permanent residence was Sāvatthi (DA.ii.399), and he often visited the Buddha at Jetavana, consulting him on many topics, such as: results of actions (A.i.56), sandiṭṭhaka-nibbāna (A.i.157), tevijjā-brahmins (A.i.166), fearlessness of death (A.ii.173), the ideals of various classes of persons (A.iii.362), true celibacy (A.iv.54), the Paccārohani ceremony (A.v.233 ﬀ., 249 ﬀ.), the efficacy of gifts (A.v.269 ﬀ.), and eternalism and annihilation (S.ii.76). He had a white chariot with silver fittings and white trappings drawn by four pure white mares. He would drive about in this, wearing white garments, turban-cloths and sandals and fanned by a white fan. The reins, the goads and the canopy were also of white. His chariot was considered the finest in all Sāvatthi (S.v.4 f; cp. M.i.175 and ii.208).
Buddhaghosa says that Jāṇussoṇi was not his personal name but the name of the rank he held as chaplain to the Kosala king. MA.i.90; according to AA. (i.308) it was the name of any noble family, members of which held this rank. Cp. Govindiye abhisiñci (at D.ii.231).