Helgo Nikolaus Zettervall, older spelling Zetterwall, (21 November 1831 in Lidköping – 17 March 1907 in Stockholm) was a Swedish architect and professor of the Royal Swedish Academy of Arts. He is best known for his drastic restorations of churches and other buildings around Sweden. He was father to Folke Zettervall. He was chief of Överintendentsämbetet 1882–97.
After studies at the Academy of Arts, he in 1860 began working on the Lund Cathedral, which was to take 20 years. Soon he was appointed for similar large scale restorations, such as Linköping Cathedral (1877–86), Skara Cathedral (1886–94) and Uppsala Cathedral (1885–93), as well as the Kalmar Castle (1886–90).
Zettervall was 1860–90 the main proponent of the Neo-Gothic architecture of church buildings. Several examples exist all around Sweden, such as in the cities of Lund, Gothenburg and Stockholm.
His influence has been much criticized. Zettervall restorations were often not intended to restore old looks, but to restore them to their, according to Zettervall, ideal look.