The Lucknow diocese erected on January 12, 1940, was part of the Diocese of Allahabad and when detached from it, comprised 10 districts of the Allahabad diocese (Lucknow, Unnao, Barabanki, Gonda, Bahraich, Sitapur, Kheri, Nainital and Almora), and two districts detached from the Archdiocese of Agra (Shahjahanpur and Pilibhit). The district of Bareilly was detached from Agra and joined to Lucknow diocese on Nov. 8, 1951, though it had already been cared for by Lucknow from September 1948, by common agreement between the Archbishop of Agra and the Bishop of lucknow. The district of Almora has been divided into two districts by Government Decree, dated February 24, 1960, the name of the other district being Pithoragarh.

At the time of erection of this diocese, Bp Angelo Poli, ofm cap, Bishop of Allahabad, was appointed Administrator of the new diocese.

Due to the war, the first Bishop of Lucknow was appointed only on December 12, 1946, and took possession of the diocese on Feb. 16, 1947.