Pope John Paul II appointed Monteiro bishop of Agartala on 11 January 1996 and he received his episcopal consecration on 26 May 1996.

[3] From 18 October 2000 to 2 October 2001, Monteiro served as apostolic administrator of the neighboring diocese of Aizawl after its bishop, Denzil Reginald D'Souza, became ill and retired.

[4][1] He chaired the North Eastern Diocesan Social Forum and was a representative of the Conference of Catholic Bishops of India on the Governing Body of Caritas India.

He previously served as chairman of Caritas India[7] for two terms until February 2020.

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