The tower at Källstads kyrka is the oldest surviving part of the building, dating from the early medieval period. It may originally have been built not as an ordinary parish church but in connection with a royal estate or the residence of a powerful nobleman, before the parish system as we know it existed. A vaulted upper chamber in the tower, with an opening overlooking the choir, allowed occupants to follow services from above—a feature that hints at its possible high-status origins.
By the 18th century the medieval church was already considered too small and outdated, and proposals were made to demolish it or merge the parish with its neighbour, Herrestad. Local resistance saw off both plans, and the church survived, if increasingly cramped, until the growing congregation prompted a full rebuilding in the 1860s. Architect Johan Nyström's new nave was joined to the old tower, whose exterior was also altered with matching gables so the two parts would appear unified.
Inside, the altarpiece structure dates from 1703, the work of Olof Wiström of Vadstena. Accounts differ slightly on some later fittings: one 18th-century description by Carl Fredric Broocman mentions a pulpit acquired in 1673 and an altar painting of the Crucifixion and Resurrection said to have been installed in 1711, while other sources attribute the 1703 altarpiece to Wiström specifically. A later altar painting depicting Christ in the Garden of Gethsemane, by Ludvig Frid, is said to have originally been erected in memory of a cavalry officer who died in 1748 and was buried in the porch.
Few medieval furnishings remain, but a font, a primitive bell (primklocka), and silver communion vessels from that era have survived the rebuilding. A slender medieval gallery structure with two delicate pillars and an elegant canopy is also preserved within the tower, offering a tangible link to the church's earliest form.
The organ has a layered history: an amateur organ builder from the parish, Per Jonsson, built an instrument in 1841 and later enlarged it in 1869 using material from an older organ acquired from another church. In 1952 a new pneumatic organ was built within the same case, incorporating some components from the earlier instrument. The church interior was restored in 1938 under architect Erik Lundberg, when the altarpiece was returned to the choir after a long absence and some window alterations were made.