Since the second half of the 17th century, the castle has been the main seat of the Biržai-Dubingiai Radziwiłł family line, which was transferred here from the Dubingiai Castle. Biržai Castle served as a major defensive structure during the wars with Sweden. The castle was reconstructed from ruins in the 1980s, in the Renaissance-Baroque style. The residential manor of the castle houses a library and a regional history museum "Sėla" (literally Selonia), founded in 1928.