He played an important role in the coup d'état of 22 January 1798 in the Batavian Republic, by general Herman Willem Daendels, which brought the radical unitarist faction of Wybo Fijnje and Pieter Vreede to power, and he helped write the Staatsregeling voor het Bataafse Volk of 1798 (the first Dutch Constitution).
The Fijnje family went to Antwerp, later to Brussels and finally to Watten (French-Flanders).
The most important Patriots, such as Wybo Fijnje, H. W. Daendels, Adam Gerard Mappa and Valckenaer lived temporarily in a castle in Watten and formed a kind of commune, that jointly bought a billiards set, restored the rooms and grew its own vegetables.