The church was probably built in the early 1100s, its walls constructed of grey fieldstone. Archaeological investigation in the late 1970s revealed that the church stands on a large prehistoric burial mound, originally some 40–50 metres wide and 5–6 metres high, which was levelled to roughly 2.5 metres when the church was built. A test excavation near the north wall uncovered a Late Iron Age grave containing cremated human, horse and dog bones along with boat rivets and a beaver claw, hinting at the site's significance long before Christianity arrived.
The medieval nave was originally paired with a smaller, straight-ended chancel, but in 1745 this was replaced by the present five-sided chancel, and the south wall of the nave was shifted outward to widen the building. A narrower, lower porch at the west end replaced an earlier timber porch that had stood on the south side, and a sacristy was added north of the chancel. The exterior is whitewashed with a slate roof, and new windows were inserted in 1853. A detached bell tower, built in 1818 to replace an older structure, houses two church bells; the smaller bell has been dated to the late 1400s.
Inside, older grave slabs removed during a 19th-century refurbishment were relaid as flooring in the porch before later being mounted on the exterior walls. The oldest commemorates a vicar who died in 1606, while a well-preserved slab honours the last vicar of Ås, who died in 1670.
Among the furnishings are a sandstone font from the late 1200s, an altarpiece made in 1688 by sculptor Georg Basselaque, and a pulpit of 1720 decorated with figures of the four evangelists. An epitaph and a hymn board, both from the mid-1700s, bear the Hebrew tetragrammaton for God's name. A brass chandelier dates from the 1700s.
Built into the north-east chancel wall is a runestone, inserted there during the 1740s rebuilding; its original location is unknown. Dated to the first half of the 11th century, it commemorates a warrior named Karl, raised by his companion Tore. A near-identical stone found in Hobro, Denmark, has led to speculation that Karl died in Denmark and that Tore raised matching memorials in both places. Around a dozen runestones are known from the wider Ås area.