The stone church at Överselö was originally built around 1200, likely replacing an earlier wooden church on the same site. It is a Gothic hall church, and its sturdy tower features small stone columns with leaf-carved capitals dated to around 1240–1250. In the 1380s, brick vaults were added, and the church was extended eastward with a new sacristy; a side chapel followed in the 1470s.
The interior is notable for its extensive medieval wall paintings. Those in the nave vaults date from the mid-1400s and depict biblical scenes and saints, while further paintings were added to the tower and south chapel in the later 1600s. A fire damaged the church in 1641, after which a pulpit was installed in the 1660s and the tower given its distinctive cap in the 1670s. A north aisle added in 1881–1882 gave the building its present cross-shaped plan.
Among the church's treasured furnishings is a Romanesque stone font contemporary with the earliest building, and a late-medieval altarpiece, probably imported from northern Germany, showing the Coronation of the Virgin flanked by the twelve apostles. A medieval wooden statue of the Virgin, the so-called "Överselömadonnan", is traditionally attributed to the Gotland-based Bungemaster workshop, though attributions of this kind are often debated among art historians. A triumphal crucifix of around 1510 is thought to originate from Lübeck.
The church holds an unusually rich collection of memorial and decorative objects: carved coats-of-arms and funeral hatchments for local noble families, notably the Slatte, Kagg and Skytte families, together with older, roughly carved memorial tablets from the late 1500s. Its bells have their own curious history — the older of the two, cast in 1638, appears originally to have been intended for a church in Kexholm (in present-day Russia/Karelia) before ending up here for reasons that remain unclear.
Of particular interest to organ enthusiasts, the church retains its 1754 organ by Jonas Gren and Petter Stråhle, said to be the oldest organ still in use within the Diocese of Strängnäs, standing alongside a larger instrument added behind it in the 1950s. Five rune stones also stand near the church, hinting at the site's much older significance in the surrounding landscape.