It was a Celtic village that in Roman times was called in Latin Laus Pompeia (probably in honor of the consul Gnaeus Pompeius Strabo) and was known also because its position allowed many Gauls of Gallia Cisalpina to obtain Roman citizenship. It was in an important position at the crossing of vital Roman roads.
In became a Catholic diocese and its first bishop, Saint Bassiano, (319-409), is the patron saint of the town (celebrated on January 19).
A free Comune (municipality) around 1000, it fiercely resisted the Milanese, who destroyed it in April 24, 1158. Frederick Barbarossa re-built it on its current location.
Starting from 1220, the Lodigiani (inhabitants of Lodi) spent some decades in realizing an important work of hydraulic engineering: a system of miles and miles of artificial rivers and channels (called Consorzio di Muzza) was created in order to give water to the countryside, turning some arid areas into one of the (still now) most important agricultural areas of the region.
Lodi was ruled by the Visconti family, who built a castle.
In 1423, the antipope Antipope John XXIII, from Lodi's Duomo, launched his bolla by which he convened the Council of Constance (end of the Great Schism).
In 1454 representatives from all the regional states of Italy met in Lodi to sign the treaty known as the peace of Lodi, by which they intended to work in the direction of Italian unification, but this peace lasted only 40 years.
The town was then ruled by the Sforza family, France, Spain, Austria. In 1786 it became the eponymous capital of a province that included Crema.
On May 10, 1796: Battle of Lodi: the young Corsican general Napoleon Bonaparte won on the river Adda his first important battle, defeating the Austrians and later entering Milan. This is why in many towns there are streets dedicated to the famous bridge (for instance in Paris 6th arrondissement, Rue du Pont de Lodi).