Initial plans in 1635 were for a student church at
Regensen, the
dormitory for students at Copenhagen University, but the following year, new plans emerged with the corner of Landemærket and Købmagergade earmarked for the church location, as it was decided to include the church in a complex extending to a church library and an astronomical observatory. The humanistically inspired combination was from a commission of Christian IV. There were three builders, namely
Hans van Steenwinckel the Younger,
Leonhard Blasius, and
Albertus Mathiesen. At the time of construction, the church was the second largest in the city, second only to the
Church of Our Lady. As the church was only intended to be used by university students and professors, it may appear oversized, but all indications are that the library space above the nave needed a certain church size. The foundation stone was laid July 7, 1637, and the Round Tower was completed in 1642. The church was consecrated on
Trinity Sunday 1656. The Copenhagen University Library was installed in the church loft in 1657. After marrying the widow of J.M. Radeck in 1685,
Christian Geist assumed Radeck's organist position at the church. During the fire of 1728, the Trinitatis Church was not as badly damaged as other churches in the city. The roof structure was ignited, a spire crashed into the library, punching a hole in some of the arches of the church. The university library was burnt. Church walls and vaults withstood the fire and subsequent repairs did not decisively change the church's appearance. A new cornice and spire were required. The new roof was covered with black glazed tiles. New dormer windows were inserted but only in one row. The interior bases and capitals of the columns and arches were repaired. All wood furnishings were replaced, and the floor was covered with tiles from
Öland. The reconstruction was in Northern Gothic-Baroque style. The church was rededicated October 7, 1731 and the remains of the university library were moved again. The furnishings were renewed with an
altarpiece and
pulpit by
Friederich Ehbisch (1731) and a large Baroque clock (1757). The church was refurbished in 1763. The Trinitatis Complex was hit during the
1807 British bombardment of Copenhagen, and damaged by major fires. Four bombs struck the library, but did not penetrate through to the church. Thanks to the efforts of churchwarden Tvermoes, injuries were minimized. Building repairs amounted to relatively modest 3,000 rigsdaler. Alterations were necessary in 1817 to celebrate the 300th anniversary of the
Reformation. It was determined that the church's main entrance, the southwest portal, did not have suitable access through the fence wall and the cemetery for the procession of priests and professors who would join the festivities, so the north face became the church front. The small shops on the corner of Landemærket were closed, as was the remainder of the cemetery north of the church. The original
portals were replaced with new ones, designed by
Peder Malling. The eastern entrance was also reopened, having been bricked up for a number of years. A major restoration was completed in 1834-35 by
Gustav Friedrich Hetsch, funded by a bequest from Christopher Hauschildt. Most of the work took place inside the building, including a
vestry, detached on the south side of the choir. The roof was refurbished in 1848-49 without affecting its appearance. In 1861, the university library moved from the church attic to
Johan Daniel Herholdt's library building in
Fiolstræde. External renovations occurred 1869-71 by a design of
Niels Sigfred Nebelong in connection with a change in the church's patronage. The sacristy on the south side of the chorus was removed and a new one built by the east gable, measuring approximately , with cut corners; it was transformed into a priest room in 1960. The notable
chamber choir dates to 1993. ==Architecture and fittings==