The church's chancel and apse, together with much of the nave, date from as early as the 11th or 12th century, making it possibly the oldest surviving church building in Norrland. Hackås kyrka is unusual in Jämtland for retaining a semicircular apse, a distinctive architectural feature. In 1770–71 the nave was extended westward, giving the building its present layout, and excavations in 1972 uncovered the remains of an earlier church tower at the western gable.
The apse contains medieval wall paintings, generally dated to the 13th century, depicting scenes from the legend of Saint Margaret. In 1601 further paintings were added to the walls by local artists Olaus Erici and Jonas Erici, arranged in panel-like fields showing the Last Supper, the visit to Christ's grave, and the Well of Life. Together these layers of decoration give the interior a distinctive and rare medieval-to-early-modern visual history for a rural Swedish parish church.
Outside stands a freestanding bell tower, built in 1752 by Per Olofsson of Dillne, a common arrangement for churches in this region. The church also has an organ built in 1874 by Johan Gustaf Ek.
Beside the church lies a spring known as the Trefaldighetskälla, or Trinity Spring, traditionally used both by local parishioners and by medieval pilgrims travelling this route on their way across the lake towards Nidaros (Trondheim). Given its proximity to Sanne gravfält, a nearby burial field with mounds and flat graves from the Iron Age, it has been suggested that the spring may originally have served as a pre-Christian cult site before its later association with pilgrimage.