The valley through which Undersåker lies once formed part of a medieval pilgrim route towards the shrine of St Olav at Nidaros Cathedral in Trondheim, a link that gives the site a long history of Christian use even though little of the earliest building survives above ground.
East of the present church stand the remains of Undersåker's medieval stone church, known as the Undersåker church ruin. Its exact date of construction is uncertain, though parts of the surviving walls may date from the later thirteenth century. The medieval church was burned during the Baltzar feud in the seventeenth century but was rebuilt, only to be demolished when the new church was raised in the 1850s. Today the remaining walls stand one and a half to two metres high and are built of granite and limestone; an 1828 drawing shows the church as it appeared shortly before demolition, with a sacristy to the east, a porch to the west, and a freestanding bell tower nearby. The ruin was archaeologically investigated in 1952 and later conserved in stages.
The current stone church was built in 1850–56 by master builder Anders M. Svensson of Östersund, to designs by the architect Albert Törnqvist. It is a neoclassical building with a rectangular nave, a straight-ended chancel to the east, an attached sacristy, and a west tower topped by a lantern cupola with a pointed spire. The rubble-stone walls are rendered white, and the tall, round-arched windows give the interior a bright, airy character. Inside, the barrel-vaulted ceiling and closed box pews date largely from the time of construction, though the church was substantially remodelled in 1936–37 under a programme associated with county antiquarian Eric Festin, when a north doorway was blocked (its outline is still visible outside) and a new sacristy entrance was created.
Several furnishings reflect different periods of the church's life. The altarpiece, depicting the women at Christ's tomb, was painted by Göran Sundin in 1854–55 and is flanked by images of Peter and Paul; the altar structure itself was carved around the same time by Sundin and the sculptor Söderqvist. An older altarpiece from 1671, thought to be the work of Anders Olsson of Hållborgen, has been retained and now stands against the north wall in front of the blocked doorway, forming part of a simple baptismal arrangement. The wooden font, of a type associated with Jämtland and carved with a pelican motif, dates from the 1680s and is among the oldest furnishings to survive from the earlier church.
The organ case on the gallery was carved by Olof Andersson and Jonas Olofsson of Hålland in 1873–74, though the organ mechanism itself was renewed in 1969, and a smaller chancel organ was added in 1988.