Wambunya was consecrated as the third Bishop of Butere on 6 October 2013,[10] succeeding Horace Etemesi (1993–2003) and Michael Joshua Sande (2003–2013).[11][12] As Bishop of Butere he attended and led a seminar at the 2018 Global Anglican Future Conference, but he would later criticise the movement, saying in 2020 "Personally, I think the Gafcon axis has become obsessed with the matter of sexuality."[13][14]
In 2020 he left Kenya and his episcopal role, and in September was appointed vicar of St Paul's Church in Slough, a 'resource church' in the Church of England Diocese of Oxford;[15] he also became an honorary assistant bishop of that diocese in 2021.[16]
In September 2024, Wambunya was formally rebuked by the Church of England after ordaining Revd Wamare Juma of the Revealed Evangelical Mission, a "non-denominational para-church" not in communion with the Church of England, as a bishop in a service in Germany in April of that year.[19][20] He apologised, attributing his actions to his "lack of understanding of the polity of the Church within which I am now serving".[21]