When Västervik was founded at its current location in 1433 by Eric of Pomerania, the inhabitants were granted four tax-free years, the first of which was to build a church. Services were held here for nearly 500 years, with the last high mass on the Feast of Christ the King (Domssöndagen) in 1905. The new church, St Peter's, was consecrated on the first Advent of the same year.
Since then, St Gertrud's was used for various purposes, including for grain storage during the First World War. Eventually, the idea to restore the church as a place of worship emerged, and St Gertrud's was re-consecrated on 18th June 1933.
The church's original tower, destroyed by lightning during a service in 1762, was replaced in the 1780s by the current one, designed by the renowned architect Carl-Fredrik Adelcratz. Among the church's many valuable artefacts is a Wistenius organ from 1743, considered one of Sweden's most precious organs.