The oldest surviving fabric is found in the thick stone walls of the nave's western part, likely dating from the original medieval building, which is thought to have had a narrower, straight-ended chancel. The present three-sided chancel was built out to the full width and height of the nave in 1731, when the interior also received a wooden vaulted ceiling. Medieval churches in the area rarely had towers, and Håby kept this plain profile until 1869, when the current wooden west tower with its pointed spire was added; its ground floor now serves as a porch. Before the tower was built, the bell hung in a separate red-painted timber bell-frame on a nearby hillside.
Three bells now hang in the tower, including one traditionally known as the Prästeklockan ("Priest's Bell"), said to be plain and uninscribed, alongside the Mellanklockan and Storklockan. The lintel above the chancel doorway is medieval, as is the soapstone slab set into the altar, both surviving from the church's earliest phase.
The furnishings show an unusual back-and-forth in taste. The altarpiece framework, font and pulpit date largely from the first half of the seventeenth century and are attributed to the woodcarver Jörgen Larsson, with the pulpit's sounding-board added in 1692. In 1877 these older pieces were replaced with newly made Victorian equivalents, only for the 1915 restoration to reverse the decision and reinstate the seventeenth-century originals in preference to the newer work — a telling example of changing attitudes to heritage. The chancel doorway itself was widened during the 1731 rebuilding, later blocked, and reopened again in a 1939 restoration overseen by Axel Forssén, which also aimed to recreate an eighteenth-century-inspired colour scheme for the interior; a sacristy built in 1871 was demolished at this time and replaced by the current one.
The west gallery dates from the church's early building phase and runs along the nave's western wall. Its painted panelling, including figures of the apostles, was decorated in 1915 by an artist whose name is given differently in surviving accounts — as either Martin Bernhard Wallström or Teodor Wallström — who is also recorded as having conserved several other furnishings that year. The altarpiece's original central painted section no longer survives; the panel now in place dates from 1939, set within the older, richly carved architectural frame.