Fidag is founded in Martigny in 1959 by André Devanthéry and opens its first branch in Sion in 1971. As the company develops, other branches open up one after another. The first branch outside the canton of Valais opens in Geneva in 2012
In 1999, Fidag is awarded ISO 9001 certification. In 2011, Fidag obtains final accreditation as an auditing company from the FAOA. One year later, in recognition of its social and environmental responsibilities, it obtains ISO 14001 certification and the labels Entreprise Citoyenne and Valais Excellence.
In 2016, Fidag acquires 100% of the share capital of Cabinet Fiduciaire et Fiscale, Dino Venezia SA in Lausanne. In 2019, it takes a 40% stake in Fidag Jura SA, created from the merger of Fiduciaire Juravenir SA and Transjurane Holding SA. At the beginning of 2020, Fidag launches Fidag Genève SA with two promising young professionals.