The first major engagement of the Second Italian War of Independence, it was fought between Austrian troops commanded by Field Marshal Philipp von Stadion und Thannhausen against Piedmontese cavalry and French infantry headed by General Élie Frédéric Forey.

Forey's division, accompanied by three Piedmontese cavalry regiments commanded by General Maurizio Gerbaix de Sonnaz [it], engaged Stadion's army corps at Montebello.

Karl von Urban's column advanced rapidly along the main road towards Voghera, repelling the Sardinian Guardia Nazionale at Casteggio, and arrived at the village of Montebello at 1:30 p.m. on 20 May.

A short distance to the north, two other columns under Franz Xaver von Paumgartten [de] and the Prince of Hesse moved slowly on country roads.

[4] For his part, Hesse was held in check between Casatisma and Oriolo by the Aosta light cavalry regiment and a pair of battalions, which his troops outnumbered three to one.

[1] On 21 May, Napoleon III received a telegraph stating, "The Austrians have attacked, on the 20th, with approximately 15,000 men the advanced posts of Marshal Baraguey d'Hilliers.

They have been repulsed by Division Forey, which conducted itself admirably and liberated the village of Montbello, already famous..." Disconcerted, Gyulay deployed his corps further south.