Catholicism was thin on the ground in this corner of the delta for most of its history. Before 1954, the provinces of An Giang and Kiên Giang together held roughly 30,000 Catholics spread across about ten parishes, a scattering among a rice-farming population that was overwhelmingly Buddhist. Then came the partition of Vietnam and the great movement of people southward, and everything changed within a decade. Families from the north settled along the Cái Sắn canals west of Long Xuyên, on land that had to be drained before it could be farmed, and the parish rolls swelled. On 24 November 1960, Pope John XXIII issued the bull Christi Mandata, carving the Diocese of Long Xuyên out of the two provinces and naming Micae Nguyễn Khắc Ngữ its first bishop. He would hold the post for thirty-seven years.

Work on the building had already begun in 1958, under the direction of Father Piô Nguyễn Hữu Mỹ. Once the diocese existed, the plans grew: the finished church runs 60 metres long, 18 wide and 20 high, with the bell tower carrying the eye far above that. For its first twelve years the diocese made do with the Church of Saint Thomas, a modest structure dating from 1903, which served as cathedral until 1972. The new church took over the following year. A large statue of the Virgin stands on the façade — she is the Queen of Peace the building is named for, and the reason it is also known simply as the Regina Pacis. Nothing about the design reaches for the French colonial gothic of Saigon's Notre-Dame; this is a church of the 1950s and 1960s, built by and for a congregation that was still settling the land around it.

The cathedral does not have Long Xuyên to itself. The town grew from a market established in 1789 beside the Tam Khê canal, and it kept the habits of a market: everybody trades with everybody. The floating market still forms on the Hậu at dawn, boats nosing together with vegetables and rice stacked on the decks. Hòa Hảo Buddhism — a reformist movement that dispensed with temples, monks and ceremony in favour of prayer at home — was founded in An Giang in July 1939 by Huỳnh Phú Sổ, in the village that gave the faith its name, and it spread through the delta within a few years. A Cao Đài temple stands in town as well. Some 286,140 people lived here as of 2022, and across the whole diocese roughly 233,018 Catholics form about five per cent of the population — a visible minority, well organised, running 164 parishes.

On 12 June 2025 Vietnam's National Assembly passed Resolution 202/2025/QH15 and Long Xuyên stopped being a provincial capital. Kiên Giang was folded into An Giang to create a province of nearly five million people, with the seat of government moved to Rạch Giá on the coast; Long Xuyên became one ward among fourteen. There is a quiet symmetry in it. The diocese that Rome drew in 1960 covered precisely those two provinces, An Giang and Kiên Giang, and had spent sixty-five years operating across a boundary the state has now erased. The cathedral's jurisdiction did not change at all. Only the map around it did.