It all started in 1946:
June 2nd, 1946, was the day Italians voted to abolish the monarchy, and the Republic of Italy was born; hence Republic Day. After an 85-year monarchy, which had for the most part been very popular with the people, a referendum resulted in 12,717,923 votes ‘for’ and 10,719,284 votes ‘against’.
Republic Day changed dates for 24 years In March 1977, Italy’s economy wasn’t doing so well, and all its public holidays were thought to be having a negative impact.
So to avoid affecting business, Republic Day was moved to the first Sunday in June.
The first Sunday of June had a long history as Italy’s national holiday; before Italy became a Republic, this holiday was known as the Feast of the Albertine Statute – the constitution of 1848, which was seen as the foundation of the Kingdom of Italy.