Herman Ernst Henrik Gesellius was born on 16 January 1874 in Helsinki to a family of wholesaler Herman Otto Gesellius and Emilia Caroline Auguste Struckmann.

Gesellius took matriculation examination from the Swedish Normal School of Helsinki in 1893 and studied architecture at the Polytechnical Institute of Helsinki. Gesellius received his diploma of architecture and established an architecture office together with Eliel Saarinen and Armas Lindgren in 1897.

The Exposition Universelle 1900 in Paris was the breakthrough for the architect trio. The Grand Duchy of Finland had its pavilion at the exposition, designed by Gesellius, Lindgren and Saarinen. The National Museum of Finland, based on the winning entry of the architecture competition in 1902 and completed in 1910, is the office’s main work, along with the atelier home Hvitträsk.

In the early years of the 1900s, Gesellius, Lindgren and Saarinen designed and built an atelier home Hvitträsk to Kirkkonummi, 30 kilometres west from Helsinki. Hvitträsk was completed in 1903, but the architect trio’s collaborative practice lasted only two more years. In 1905 Armas Lindgren moved out of Hvitträsk, and the office was laid down when Saarinen’s and Gesellius’ private lives got turbulent. Eliel Saarinen separated from his wife Mathilda Saarinen (nee Gyldén) in 1904. Mathilda Saarinen went on to marry Herman Gesellius, and Eliel Saarinen married Gesellius’ sister, textile artist Minna Carolina Louise “Loja” Gesellius.

Gesellius fell ill of tuberculosis, and his career was cut short. One of his main works, along with the works of Gesellius Lindgren Saarinen, was the Wuorio House in Helsinki.

Herman Gesellius lived in Hvitträsk for the rest of his life, he died at the age of 42, on 24 March in 1916 of cancer. Gesellius is buried in the Hvitträsk estate.