Prior to the establishment as a local church, the present-day Diocese of Pasig used to be a part of the Archdiocese of Manila (largely under the Ecclesiastical District of Makati). The Vicariate of Santo Tomas de Villanueva was then under the Diocese of Antipolo. The oldest parishes, built during the Spanish colonialization period, were in Pasig (Immaculate Conception), Pateros (San Roque), and Taguig (Saint Anne). In 1953, the community of Santolan, Pasig was granted a parish of their own, Santo Tomas de Villanueva Parish, which was followed by the establishment of new parishes in Rosario and Bicutan (1963), Tipas and Bagong Ilog (1969), and Barrio Capitolyo (1976). The northeastern side of Pasig, which comprises the barangays of Manggahan, Santolan, De La Paz, Santa Lucia, and Rosario, was given to the newly established Diocese of Antipolo in 1983. Between 1985 and 1995, six chapels of the Immaculate Conception Parish were elevated as independent parishes.

Parishes belonging to the Vicariate of the Immaculate Conception and to the municipalities of Taguig and Pateros were part of the Ecclesiastical District of Makati, which was then headed by Manila Auxiliary Bishop Crisostomo Yalung. In October 2001, these parishes were carved out to form the new Ecclesiastical District of Pasig, with Nestor Cariño, then Secretary-General of the Catholic Bishops' Conference of the Philippines (now bishop-emeritus of Legazpi), as its first district bishop. Between the years 2000 and 2003, in preparation for the erection of the new diocese, some juridical changes to the district took place. Barangays San Antonio and Oranbo, which formerly belonged to Saint Francis of Assisi Parish in Mandaluyong, were turned over to Holy Family Parish. The military chapel of Our Lady of the Assumption in Fort Bonifacio was turned over by the Military Ordinariate to the Archdiocese of Manila in 2000 and was renamed Saint Michael Chaplaincy. Saint Joseph Chapel in Upper Bicutan, Taguig, which belonged to San Martin de Porres Parish in Parañaque City, became an independent parish under the District of Pasig in 2002.

On June 28, 2003, few months after carving out the dioceses of Paranaque and Novaliches from the Archdiocese of Manila, Pope John Paul II decreed the erection of three more new dioceses in response to the surging pastoral needs of the faithful of the archdiocese. With the promulgation of the Papal Bull Deus Caritas, the Pope officially established the new Diocese of Pasig and appointed Francisco Capiral San Diego, then bishop of San Pablo, Laguna, as its first bishop. The Vicariate of Santo Tomas de Villanueva was separated from the Diocese of Antipolo to be included in the new diocese. The diocese was canonically erected on August 21, 2003, with the installation of Bishop San Diego in the presence of the Apostolic Nuncio, Archbishop Antonio Franco, Manila Archbishop Cardinal Jaime Sin, and the bishops gracing the occasion. Bishop San Diego named the district's Episcopal Vicar, Rodolfo Gallardo as the first Vicar General, Roy Rosales as the first Chancellor, Pedro Enrique "Betbet" Rabonza IV as Judicial Vicar, Amando Litana as Superintendent of Catholic Schools, and Manuel Gabriel as the Diocesan Pastoral Director.

On December 2003, Msgr. Gallardo was installed second rector of the Immaculate Conception Cathedral-Parish. After he retired as Vicar-General and cathedral rector in February 2005, he was succeeded by Bishop San Diego as acting parish priest and rector. The bishop named Ramil Marcos, his private secretary and Vice-Chancellor, as the second Vicar General of the diocese and Roy Rosales as the fourth rector of the cathedral. In 2006, he appointed Orlando Cantillon as the new Vicar General.

During his term, Bishop San Diego worked for the improvement of the Catholic cemetery and the construction of the bishop's residence and diocesan offices within the vicinity of the cathedral. He started a retirement plan fund for the clergy and summoned a general pastoral assembly for lay leaders in the diocese. Due to the shortage of parish priests, he entrusted a number of parishes to guest priests as priests-in-charge or administrators. His term was marked by the papal canonical coronation of the image of Our Lady of the Immaculate Conception of Pasig in the cathedral on December 7, 2008, the solemn declaration of San Roque Parish in Pateros as the Diocesan Shrine of Santa Marta on February 7, 2009, and the establishment of Tanyag Chapel, which belonged to Sagrada Familia Parish, as a quasi-parish (Our Mother of Perpetual Help Quasi-Parish) on September 8, 2010.

On December 21, 2010, Pope Benedict XVI accepted San Diego's retirement as bishop and named Manila Archbishop Cardinal Gaudencio Rosales as concurrent Apostolic Administrator of the diocese. On April 20, 2011, the Pope appointed Mylo Hubert Claudio Vergara, bishop of San Jose, Nueva Ecija, as the new, second bishop of Pasig. During his term, Bishop Vergara strengthened the lay evangelization programs in the diocese, invited some religious orders to administer a number of parishes in the diocese, and oversaw the inauguration of the Tahanan ng Mabuting Pastol (House of Good Shepherd) Building within the vicinity of Santa Clara de Montefalco Parish to house the new bishop's residence and diocesan offices on April 24, 2017. On September 15, 2012, he established San Vicente Ferrer Quasi-Parish in Palar Village, Barangay Pinagsama, C-5, Taguig City and later elevated to the status of full-fledged parish the quasi-parish of Bagong Tanyag (2015), the chaplaincy in Fort Bonifacio (2017), and the quasi-parish of Palar (2018).

Ang Escudo ng Diyosesis ng Pasig ay sumasagisag sa paanyaya ng Inang Simbahang Katolika sa lahat, kasama ng mga pangunahing patron sa sina Santa Ana, San Roque, Santa Marta at ng Birheng Maria, na sama-samang maglakbay sa ilog ng buhay patungo sa Panginoong Diyos.

Ang kabuuan ng escudo ay nahahati sa dalawang bahagi ng tatlong pares na maalong guhit na kulay puti at bughaw na sumasagisag sa ilog na nag-uugny sa tatlong baying sakop ng Diyosesis ng Pasig. Sa ilog ding ito nagsimula ang sibilisasyon, kultura, hanapbuhay at pananampalataya ng mga naunang mamamayan, at patuloy na sumasagisag sa pagbabago ng panahon, ng kalikasanb at ng mga tao. Sinasagisag naman ng mala-langit na bughaw ang kalangitan at ang luntiang bahagi naman ay sumasagisag sa ugat ng diyosesis bilang isang masaganang kabukiran na dinidilig ng ilog Pasig.

Sa may gawing itaas ay matatagpuan ang titik na A at M na pinaliligiran ng labing dalawang bituing ginto at napapaibabaw sa ginintuang buwan na sumasagisag sa Birheng Maria, ang pangunahing patron ng Pasig sa titulong Our Lady of Immaculate Conception.

Samantala, ang Taguig, ay kinakatawan ng kanyang pangunahing patrona na si Santa Ana na sinasagisag ng aklat na nakabukas. Madalas na inilalarawan si Santa Ana na nagtuturo sa kanyang anak, ang Mahal na Birhen, at higit na mahalaga sa kanyang itinuro ay ang tungkol sa tipan ng Diyos. Ang aklat na nakabukas at may dalawang tali na sumasagisag naman sa letrang Griego, Alpha, ang unang letra ng alpabeto na katumbasng Hebreong Aleph na sagisag ng Diyos bilang ugat at simula ng lahat. Ang uhay ng palay naman ay sagisag ng bunga ng pawis ng mga taga-giik na pinaniniliwalang pinanggalingan ng pangalan ng bayan ng Taguig.

Ang tungkod ng penigrino na may nakasabit na sisidlan ng tubig ay sumasagisag naman kay San Roque, ang pangunahing patron ng Pateros. Samantalang ang palaspas at Krus naman ay ang simbulo ni Santa Marta, ang patrona ng mga mag-iitik at magbabalut, ang hanapbuhay na pinagkakilanlan sa bayan ng Pateros.

Nakabitin sa likod ng escudo ang balat na sinturong sinusuot ng mga Agustino na unang naghatid ng Ebanghelyo sa Pasig. Pinaniniwalang nang mailibing na ang Birhen Maria, dinalaw ni Santo Tomas ang kanyang libingan. Nguni’t anong laking taka ni Santo Tomas nang matagpuan niyang walang laman ang libingan maliban sa tumpok ng rosas at isang sinturon. Sa pamamagitan ng sinturon ay maraming nagawang himala si Santo Tomas. Napasakamay ni Santa Monica ang sinturon at dahil sa kanyang debosyon sa Mahal na Birhen, nagbagong loob ang kanyang anak na si Agustin.

Sa ibabaw ng escudo ay ang pulang mitra, na simbulo ng Panginoong Hesukristo bilang Pari.

“Pasce agnos meos”, literally translated as “Feed my lambs” (Jn. 21, 17) – this is our Bishop’s motto which expressed his faith like that of Peter who was called by Jesus to translate his love for him into action. Bishop Mylo Hubert Claudio Vergara officially takes over as the second Bishop of Pasig with the Canonical Installation on June 23, 2011, 3 p.m. at the Immaculate Conception Cathedral, Malinao, Pasig.

The symbol on the left side of the shield represents the Diocese of Pasig. On the right side are his personal symbols: the 12 stars symbolizing the Holy Apostles and the Seminary where he received seminary formation, the symbol of Mary as the Immaculate Conception, Patroness of both Archdiocese of Manila and Diocese of Cubao, the meek lamb symbolizing the offering his life as a sacrifice for the people he is called to minister. It is also symbolical of Jesus, the Good Shepherd and the parish in Novaliches where his vocation flourished.

The three symbols on the lower crest represent the saints who molded his vocation – Ignatius of Loyola, John of the Cross, Teresa of Avila, Therese of the Child Jesus, and Thomas Aquinas.