He opposed the claims of the legitimately-elected patriarch Hnanishoʿ I (686–98), who had offended the caliph ʿAbd al-Malik with a tactless remark about Islam.
Hnanishoʿ's successor Sliba-zkha (714–28) removed Yohannan's name from the diptychs, and he is not included in the traditional list of patriarchs of the Church of the East.
When ʿAbd al-Malik, son of Marwan, the king of the Arabs arrived in the land of Senʿar [Babylonia], Hnanishoʿ came to meet him and offered him the usual presents.
Meanwhile Yohannan had borrowed large sums of gold in order to bribe the governor of ʿAqula, and when the time came for repayment was unable to meet his obligations.
[1] Bar Hebraeus also mentioned that Yohannan's name was removed from the list of Nestorian patriarchs by the catholicus Sliba-zkha: He removed the name of Yohannan Garba from the diptychs, reconsecrated the bishops consecrated by Garba, and put back the name of Hnanishoʿ, who had been oppressed by calumny, alongside those of the rest of the catholici.