The residents of the town pronounce the final "t" in Nicolet, however people outside of the region do not.
The town took its name from Jean Nicolet, a French explorer and clerk of the Company of One Hundred Associates, who explored the Great Lakes region west to Wisconsin. Despite never having lived there, he explored the area during the seven years he lived in Trois-Rivières. The area was originally settled by the Abenaki tribe, who knew it as Pithigan or Pithiganek, meaning "entrance". French colonial settlement of Nicolet area began in the late 17th century, with Pierre Monet de Moras constructing a seigneurial manor on what is now known as Moras Island. Rights to the territory of Nicolet was accorded in 1672 by Jean Talon, passing through several hands in the next thirty years. Significant land development began at the opening of the 18th century, with the construction of the Saint-Jean-Baptiste Jesuit mission in 1701, a chapel in 1710, a presbytery in 1722, and a second church being raised in 1740.
The first Acadian settlers arrived in 1756, after their expulsion by the British, who had defeated the French in the Seven Years' War. During the late 18th century, the area eventually became a major centre for the Acadian diaspora. Some Acadian refugees continued south into the United States.
Development continued with the construction of a third church in 1784, the first elementary school in 1801, and establishment of the Nicolet Seminary School in 1803. The parish of Saint-Jean-Baptiste-de-Nicolet was officially opened in 1831; Nicolet's episcopal seat was established later in 1885.
A fourth church was constructed in 1873, suffering the collapse of its steeple shortly thereafter. Attempts to reconstruct it failed due to the weakness of the building's structure. Construction of the second cathedral began in 1897, but a part of the building collapsed in 1899. On June 21, 1906, a fire destroyed an area of the town including both cathedrals and the headquarters of the Sisters of the Assumption. Reconstruction began soon afterwards, with the new headquarters of the Sisters of the Assumption and a girls' school being inaugurated in 1908. An agricultural school was added to the Seminary in 1938, and a test centre for the Canadian Armed Forces was established in 1952.