Dr John was nominated by Her Majesty the Queen to become the sixth person to take up the post and succeed the late Bishop John Wraw.
He used the occasion to set out his mission of letting people know that God is with everyone in challenging times.
Dr John is currently Archdeacon of Barking in East London. He has been described by Rt Rev Stephen Cottrell, the Bishop of Chelmsford as "a wise and gifted theologian and pastor".
Dr John said he's "humbled and honoured" to accept his new position and his new mission to Essex will be one of "serving the churches and communities".
He added: "I am passionate about the Christian faith that can transform individuals, communities and institutions, and about communicating that faith through pastoral care, teaching and community engagement.
"God is about human flourishing. He is there for every Essex Man and every Essex Woman.
"I am aware of the social, economic and cultural challenges faced by the communities in the area. I am committed to working with and serving the churches and communities in this part of Essex."
Bishop Stephen Cottrell said Dr John will do well in his new role as he "has won the trust and affection of the parishes, supported the mission of the Church, and helped ensure each community was served effectively" as the Archdeacon of Barking.
According to the Diocese of Chelmsford, a consecration ceremony will take place on 3rd July.
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