A church is recorded on this site since the Middle Ages, though nothing is known of the original building. A wooden church noted in the 1700s had a flat ceiling and a small tower housing a bell rising from the roof itself. A separate bell tower was built in 1735 by the farmer Lars Abrahamson of Helgum. The present timber church dates from 1817–1818, with its tower following in 1821; the builder is named as Jon Mattsson of Avaträsk.
Local tradition holds that an earlier Fjällsjö church once stood at Sunnansjö, and that when it was decided to move the church across the river to its present site in Backe, one of the church bells fell into the water during the crossing. Its location could later be identified, and numerous attempts were made to recover it over the years, but according to the story the bell always slipped from the salvagers' grasp just as it was about to be raised to the surface.
Among the church's furnishings is a wooden figure of the Madonna dating from the 13th century, and an altar cabinet in the form of a 16th-century triptych. The current pulpit dates from 1863, while an earlier pulpit from 1782 is preserved in the parish's church museum. A set of implements for administering communion to the sick dates from 1766.
An earlier altarpiece, painted in 1933 by Olle Hjortzberg and depicting the angel's greeting after the Resurrection, now hangs on the church's south wall rather than above the altar. The church acquired an organ in 1884.