Before 100 BC Celts lived in the area. Later the Franks came into this area as graves from the 7th century prove. The first written document is the Life of the first bishop of Münster. It describes how bishop Ludger walked from Budica through the forest of Hamrithi. Budica is the former name of Büttgen which now is a village belonging to the town Kaarst. Kaarst was mentioned for the first time as 'Karlesforst' in the year 1218. Karl was a very common name for frankish nobles. The most famous of them was king Charlemagne ('Karl der Große'). Lore says that Kaarst was founded by Charlemagne but this is not proven. Probably, Charlemagne used the forest of Hamarithi in order to hunt with his closest companions.
Kaarst and Büttgen had a prospering Christian life in the Middle Ages and they both have churches built in the 12th century. In the following centuries the area was influenced by the big wars and both villages were destroyed by Charles the Bold duke of Burgundy (Karl der Kühne, 1474–1475), in the 'Truchsässische Kriege' (1585 bis 1586) and in the Thirty Years' War (1618–1648). On a farm near Büttgen Jan van Werth was born in 1591 who became a famous general. During the Thirty Years' War, Kaarst got attacked several times by hostile armies, e.g. the one of Northern-Hesse (Northern-Hesse collaborated with Sweden and France, whereas the southern part of Hesse did not). Some time in 1642, a Hessian troop entered the city murdering bestially the local preacher and destroying the church's accommodation. It is not proved, but a legend says that a few Hessian soldiers had been somehow caught by farmers who rapidly found out what had happened in the church, reasoning them to lynch the aggressors immediately. From 1794 till 1814 Kaarst was part of France during the reign of Napoleon I. After conquering the Rhine area the French restructered the districts in 1798 and the city became a part of the Kanton Neuss. A relic of Napoleon I is the Nordkanal, a channel that was designed to connect the rivers Maas and Rhine.
In 1936 Büttgen had some 4,400 inhabitants and Kaarst only some 2,000.
In 1975 the villages Kaarst and Büttgen were annexed with the city of Kaarst with now having 33,500 inhabitants.
In the 2015 communal elections, Dr. Ulrike Nienhaus (CDU) was elected mayor of Kaarst with 55.8 percent of the valid votes. With this result she is the first femal mayor of Kaarst. She won the election during September 2015 against Christian Gaumitz.