The house of merchant Johan Sederholm at the corner of the Senate Square is the oldest building in Helsinki city centre. The stone house, built in 1757, was in its time the most impressive private home in Helsinki. It was probably designed by the German-born master builder Samuel Berner. The building of the house was an indication of Helsinki's growing affluence in the mid-18th century, when the construction of the Suomenlinna sea fortress began. There was a shop and business premises on the lower floor of the house and an apartment upstairs. The vaulted cellars were used as storage room. Sederholm's descendants owned the property until 1822, after which the property had a number of different owners.
The architect Konstantin Kiseleff bought the house in 1865 and drew up a renovation plan, led in 1866, the windows were enlarged, balusters installed under the upstairs, windows and three doors were inserted into the facades facing the street. In the 1850s and 1860s the building housed a tobacco factory, a girls' school, various restaurants and a bakery. Several small shops occupied the ground floor. Tenants also lived in the house. The Kiseleff family owned the property until 1912. The City of Helsinki acquired the building in 1949 and converted it for the use of the city court. When the city court moved elsewhere in 1985, the building passed to the City Museum.
The Sederholm House was repaired without changing its external appearance or the interior layout. The facades look like they did originally, apart from the windows. Changes made to the rooms between 1866 and 1950 were left as they were. One room on the second floor was decorated in 18th-century rococo style. The museum was opened to the public in 1995.