After his invasion of Gallia, Gaius Iulius Caesar made the Rhine river the border between the Roman Empire and Germania. Some small areas east of it were later invaded and added to the Roman province of Agri Decumates. As it was attacked more and more it was given up in the second half of the third century and a military camp was founded, named "Vicus Iulii" ("Village of Julius/Julius' Village). It was supported up to the fourth century.
The first record of the name "Germersheim" is from 1090, when it was named in the Sinsheimer Chronik (Chronicle of Sinsheim). The German King Rudolph von Habsburg (Rudolf of Habsburg) gave Germersheim city rights in 1276 (18 August). There is a legend which says that he, as a sick man, rode from Germersheim to Speyer to die there and not in Germersheim.
Having been nearly destroyed in the times of the plague and the Thirty Years' War Germersheim was burned down by French troops in 1674. Only the crypt and the foundations of the Catholic Church survived.
From the year 1797, Germersheim belonged to France, incorporated into the newly created Mont-Tonnerredepartment in 1798. It was conquered by Bavarian troops in 1814. After being retaken in 1814, Germersheim's Bavarian rulers started to build a fortress in 1831. It was completed in 1855, although excavations for underground passages continued until 1861. By this time, however, the fortress had become outdated, as artillery had improved greatly in the thirty years since work began. The fortress was destroyed in 1921/22 as a result of the Treaty of Versailles. Some parts still exist, such as the "Fronte Beckers", where the town's Music School is today.
General Hans Graf von Sponeck, who ordered the retreat of his troops from Kerch because they were going to be hopelessly cut off by the Russian landings at Theodosia, on the Crimean Peninsula, and against express instruction of his superior officer in the winter 1941, was interned here in the fortress after Hitler had commuted his death sentence to six years detention. In the purge following the failed assassination attempt on Hitler Graf Sponeck, although not involved, was shot. Today, a street in Germersheim is named Hans Graf Von Sponeck Straße in his honour.
In 1972 the Second British Rock Festival was held here. After learning of the festival plans, the city authorities tried to stop it, on the grounds that the town and its population (at the time around one tenth of the number of expected concert-goers) could not accommodate such a large crowd. However, the city soon realized it could not stop the surge of people into Germersheim and relented.