A constitutional referendum was held in France in 1793 and 1794. While most voting took place in July 1793, the last day of voting was not until 4 April 1794 when residents of Châteaulin voted. The new constitution was approved by over 99% of voters. However, due to the 13 Vendémiaire, the constitution was never enacted.
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Text from the Wikipedia article “French constitutional referendum, 1793”, available under CC BY-SA 4.0.