Bishop John comes from the ancient Christian community in Kerala, South India, and was ordained into the Church of North India in 1994. He moved to the UK in 2001, serving in roles in the Dioceses of Rochester and Chelmsford.
Among other roles, Bishop John is the Chair of Churches Refugee Network of Churches Together in Britain and Ireland.
He follows Bishop Paul Bayes who retired in February 2022.
He said: "As a follower of Christ coming to lead a diocese that aspires to be a bigger church to make a bigger difference, I want to proclaim and live out a message of hope, peace, and justice."