The Museum Siam building, formerly the Ministry of Commerce headquarters, stands as a symbol of Siam’s transition into the modern era. Designed by Italian architect Mario Tamagno in a Western classical style, the three-storey building features three projecting bays and was constructed with reinforced concrete — a modern material and technology of its time. Completed in 1922, the building initially served as the Ministry of Commerce.

In the reign of King Vajiravudh (King Rama VI), the Ministry of Commerce was a newly established government agency critical to managing international trade and introducing modern commercial sciences to Siam. The ministry implemented Western-style administrative systems such as the Division of Mineral Separation, with a laboratory to develop new exportable mineral products; the Statistics and Forecasting Division, which analysed global market trends for crops; and the Weights and Measures Division, which standardised measurements according to international rules.

The building’s architecture and its use embody Siam’s embrace of modernity and global commerce, representing the nation’s shift from traditional ways to an urban, modern lifestyle.

As the ministry expanded, its offices became insufficient, prompting a move to Nonthaburi in 2004. In 2005, the National Discovery Museum Institute was granted use of the building, which was renovated and opened to the public as Museum Siam in 2008.