The Poona Diocese consists of the civil districts of Pune, Satara, Solapur, Sangli, Kolhapur, Ratnagiri and Sindhudurg.
 
Around 1790, the Archbishop of Goa, at the request of Dom Manuel Noronha, a Portuguese officer working in the Peshwa’s army, sent Fr Vincent Joaquim Menezes to minister to the Catholics working in the army of the Peshwas. Fr Menezes resided and said Mass in the house of Dom Noronha. In 1794, with the contribution of the Catholics in the army, a small chapel was built at Nana Peth on a plot offered by the Peshwa. The First Mass was celebrated in this chapel on Christmas Day. These were the beginning of the Church of the Immaculate Conception, commonly known as the City Church.
 
About 1800 the Vicar Apostolic of Bombay started sending his priests to minister to the Catholics in the Scindia’s army but he stopped this about 1804. In 1835 Fr Britto, a Goan priest working under the Vicar Apostolic acted as Military Chaplain in a Chapel built at Right Flank Lines, Wanowrie. In 1850, St. Patrick’s church, the present Cathedral was built.

Poona was erected into a Vicariate Apostolic by dismemberment from Bombay on March 8, 1854, and entrusted to the Society of Jesus. The Vicar Apostolic of Bombay remained Administrator till the Hierarchy was established in 1886. Bp Bernard Beider – Linden, sj, was appointed its First Bishop.
 
On October 20, 1953, the Catholics of Ratnagiri District and those of the Church of the Immaculate Conception, Pune, who formerly belonged to the Archdiocese of Goa, were placed under the jurisdiction of the bishop of Poona. On November 30, 1953 the districts of Dharwar and Bijapur, formerly in the Poona diocese were attached to the newly constituted Diocese of Belgaum.
 
On June 9, 1987 the Holy Father created the Diocese of Nashik comprising four districts, Nashik, Dhule, Jalgaon and Ahmednagar of the Poona diocese and appointed Fr Thomas Bhalerao, sj, as its First Bishop.
 
The re-dedication of St. Patrick’s Cathedral took place on October 22, 1987. The roof of the old Cathedral collapsed shortly before midnight on July 15, 1984. The outer walls and facade have been retained, but there is now a vault roof of concrete.
 
His Holiness created the Eparchy of Kalyan on May 19, 1988 which is contiguous with the Archdiocese of Bombay and the Diocese of Poona and Nashik. On August 24, 1988 Fr Paul Chittilapilly was ordained Eparch of Kalyan and the new diocese was formally inaugurated and all Catholics of the Syro-Malabar Rite in the diocese came under his jurisdiction.