An inscription in the plaster of the chancel records a consecration date of 13 August 1135, a claim supported by dendrochronological dating of the timber. If this dating is accurate, Forsby church would be the oldest precisely dated church in Sweden, though such early inscriptions and datings are sometimes debated by historians.
The church itself is tower-less, with a nave, chancel and apse, and is considered an early example of Romanesque influence reaching Sweden from Skåne. The nave was rebuilt during the medieval period. After the Reformation the building fell into long neglect and reportedly came close to ruin before being restored in the seventeenth century.
Perhaps the most striking feature of the site is archaeological rather than architectural: the church stands directly on top of a large Iron Age burial mound, some 40–45 metres across and over three metres high. Excavations carried out in 2002, during work on the parish storehouse, uncovered a lime-burning pit thought to date from around the time the church was built. The church also lies close to one of only two known 'husaby' estates in Västergötland, place-names linked to early medieval royal landholding, suggesting the area may once have been a local seat of power as far back as the late Viking Age.
Among the church's furnishings, ceiling paintings from 1745 by the Skövde artist Johan Risberg depict the Nativity, the Resurrection, the Last Judgement and the Resurrection of the Dead. According to local tradition, a fifth scene depicting Hell was later painted over after it frightened parishioners so much that they became reluctant to enter the church; this story should be treated as tradition rather than confirmed fact.
A small medieval madonna panel and a thirteenth-century silk chasuble made in Regensburg, once kept in the church, are now held at the Swedish History Museum. The church's smaller bell is medieval, bearing two blank inscription bands flanked by finely carved double crosses.
A belfry dating from 1704 and an eighteenth-century parish storehouse stand near the church, adding to the sense of a long-inhabited and layered site.