The original papal mandate was modest in scope: 'Hong Kong with the surrounding six leagues.' It was intended as a temporary jurisdiction, carved out from the Diocese of Macau in recognition of Hong Kong's new colonial status. Within two decades, the physical territory had expanded well beyond that boundary — by 1860 it included the San On District, the Kowloon Peninsula, Sai Kung Peninsula, and Nam Tau. The mission grew alongside the colony, building churches, schools, seminaries, and institutions for the sick, the elderly, and orphaned children. Four Sisters of Saint Paul of Chartres arrived on 12 September 1848 at the request of Prefect Apostolic Théodore-Augustin Forcade; their first task was establishing a home for abandoned babies, mostly girls. In 1874, the prefecture was elevated to a vicariate apostolic, entrusted to the Seminary of Foreign Missions of Milan.

By the late 19th century the Church had become deeply embedded in Hong Kong's institutional life. The Société des Missions Étrangères de Paris operated a sanatorium at Béthanie in Pok Fu Lam — a place for priests and missionaries from across Asia to recover from tropical diseases before returning to their postings. When bubonic plague swept Hong Kong in 1894, much of the population fled the city. In the aftermath, John Douglas Lapraik sold his family estate at Pok Fu Lam — Douglas Castle — to the French Mission. The building became a monastery renamed Nazareth and eventually housed one of the busiest Bible printing and translation facilities in early twentieth-century Asia. Through the 1920s and 1930s, religious orders from many traditions arrived, building hospitals and schools that would become permanent fixtures of Hong Kong's social fabric. In 1935 the Dominicans established St. Albert the Great's Priory at the foot of Mount Nicholson — a House of Studies for the entire Far East — in a district that became known as Rosary Hill.

On 11 April 1946, Pope Pius XII elevated the Hong Kong vicariate to a diocese, making it directly responsible to the pope. Enrico Valtorta became the first bishop. The Cold War years brought a different kind of pressure: in 1949, refugees fleeing the Chinese communist regime poured into Hong Kong, including large numbers of Catholics and clergy from across China. The diocese opened seven new chapels for refugees in 1952. In 1969, Francis Hsu became the first ethnically Chinese bishop of Hong Kong, a milestone in a diocese that had been led by Europeans for over a century. John Baptist Wu became the first cardinal from the Hong Kong diocese in 1988, appointed by Pope John Paul II. Joseph Zen Ze-kiun, who succeeded him as the sixth bishop in 2002, was elevated to Cardinal by Pope Benedict XVI in 2006 — and became one of the most publicly outspoken critics of Beijing's policies in the entire Catholic world.

The relationship between Hong Kong's Catholic Church and the political landscape has never been simple, and it grew more fraught after 2019. Cardinal Zen — Bishop Emeritus after his retirement — maintained consistently that he was patriotic while opposing what he described as the erosion of Hong Kong's freedoms. His views put him at odds with the approach of the Holy See, which has pursued a cautious accommodation with Beijing, and with successive Hong Kong governments; former Chief Executives Donald Tsang, Carrie Lam, and current Chief Executive John Lee are all Catholics who represent a different strand of the community's political identity. In July 2022, the Vatican's unofficial representative in Hong Kong warned that religious freedoms in the territory were under pressure from mainland Chinese authorities. In May 2023, the diocese announced it would not hold its annual commemoration of the Tiananmen Square massacre — a tradition since 1989, last observed in 2021.

The Cathedral of the Immaculate Conception stands on Caine Road in the Mid-Levels, the see church of a diocese that traces its foundation stone to the same dedication in 1842. The current bishop, Jesuit priest Stephen Chow, was appointed by Pope Francis in May 2021 — a careful appointment made difficult by Bishop Michael Yeung's unexpected death in January 2019 and the social upheaval that followed. As of August 2022, the diocese counts 395,000 local Catholics and 169,000 Filipino Catholics served by 279 priests, 36 deacons, 62 brothers, and 419 sisters. It operates schools with more than 136,000 pupils. On paper, the Diocese of Hong Kong is a suffragan of the Archdiocese of Guangzhou. In practice, it answers directly to Rome — a canonical arrangement that mirrors the larger uncertainty about where Hong Kong itself belongs.