Andreas Graf O'Reilly von Ballinlough (3 August 1742 – 5 July 1832) was an Irish-Austrian soldier and military commander of Irish origin.

[4] Reacting to the surprise French offensive, Melas ordered O'Reilly to take 3,000 troops and an artillery convoy to defend Piacenza.

On 6 June, after an 11-hour skirmish, he successfully managed to save the artillery convoy and withdraw to the west, while fending off a French column that tried to cut him off.

[6] At the Battle of Montebello on 9 June, Peter Karl Ott von Bátorkéz ordered O'Reilly to hold the village of Casteggio with six battalions and four squadrons.

Yet, when he saw O'Reilly's men come under attack, Ott ignored army Chief of staff Anton von Zach's advice and committed his corps to battle.

[7] Reinforced by Claude Perrin Victor, the French finally gained the upper hand and Ott called on O'Reilly to cover the retreat.

The units under his leadership included single battalions of the Banater #4, Warasdiner-Kreutzer #5, Oguliner # 3, and Ottocaner # 2 Grenz Infantry Regiments, plus one company of Mariassy Jägers.

[9] On the afternoon of the 13th, O'Reilly held Marengo village, which Melas intended to hold in preparation for his planned offensive the next day.

In contrast to his stout defense of Casteggio, O'Reilly's performance was weak and Victor captured Marengo after only an hour of fighting.

[10] On the morning of the 14th, the Advance Guard under Johann Maria Philipp Frimont and O'Reilly's Right Column soon found Gaspard Amédée Gardanne's French division blocking their path.

[12] While the rest of the army hammered at the main French battle line near Marengo, O'Reilly became preoccupied with Achille Dampierre's 300 to 400 Frenchmen who occupied Stortigliona Farm on the south flank.

But, the small French detachment tied up a significant part of O'Reilly's column during the day[13] Nevertheless, he earned the Knight's Cross of the Military Order of Maria Theresa on 18 August 1801.

[17] At the beginning of the War of the Third Coalition, O'Reilly led a cavalry division in the Armee von Italien of Archduke Charles, Duke of Teschen.

[18] In the Battle of Verona (1805) on 18 October 1805, Count Heinrich von Bellegarde led his corps to support Josef Philipp Vukassovich, whose division was under attack by the French.