An outnumbered Indian and British force, under the command of Major General Arthur Wellesley (who later became the Duke of Wellington), defeated the combined Maratha army of Daulatrao Scindia and the Bhonsle Raja of Berar.

After several weeks of pursuit and countermarching, Scindia reinforced the combined Maratha army with his modernized infantry and artillery as the British forces closed in on his position.

Wellesley's force, however, encountered the Maratha Army, under the command of Colonel Anthony Pohlmann, a German formerly in British service, 6 miles (9.7 km) farther south than he anticipated.

[5] The hostilities culminated in the Battle of Poona in October 1802 where Holkar defeated a combined army of Scindia and Baji Rao II – the Peshwa and nominal overlord of the Maratha Empire.

Scindia retreated into his dominions to the north, but Baji Rao was driven from his territory and sought refuge with the East India Company at Bassein.

[6] Lord Mornington, the ambitious Governor-General of British India, seized on the opportunity to extend Company influence into the Maratha Empire which he perceived as the final obstacle to Britain being the dominant force in the Indian subcontinent.

[12] However, Scindia had formed a military alliance with the Rajah of Berar with a view to bringing the Maratha leaders into a coalition against the British, and had begun to mass his forces on the Nizam's border.

[13] Wellesley, who had been given control over the company's military and political affairs in central India in June, demanded Scindia declare his intentions and withdraw his forces or face the prospect of war.

Of the other Maratha leaders, Holkar was hesitant to enter the war in cooperation with his rival, Scindia, and remained aloof from the hostilities, and the Gaekwad of Baroda placed himself under British protection.

[6] Operations in the north were directed by Lieutenant General Gerard Lake who entered Maratha territory from Cawnpore to face Scindia's main army which was commanded by the French mercenary Pierre Perron.

Wellesley was determined to gain the initiative through offensive action and told his senior subordinate, Colonel James Stevenson, that "a long defensive war would ruin us and will answer no purpose whatever".

In the meantime, Wellesley moved north from his camp near the Godavari River on 8 August with some 13,500 troops and headed towards Scindia's nearest stronghold – the walled town and fort at Ahmednagar.

The walled town, which was garrisoned by 1,000 Arab mercenaries, upwards of 60 cannon and one of Scindia's infantry battalions under the command of French officers, was captured with minimal losses after a brief action.

[21] With the fortification providing a base for future operations into Maratha territory, Wellesley installed a garrison and headed north towards the Nizam's city of Aurangabad.

Along the way he captured Scindia's other possessions south of the Godavari and established a series of guarded bridges and ferries along the river to maintain his communication and supply lines.

[23] The combined Maratha army was around 50,000 strong, the core of which was 10,800 well-equipped regular infantry organised into three brigades, trained and commanded by European adventurer and mercenary officers.

They agreed on a plan by which their two armies – moving separately along either side of a range of hills with Wellesley to the east and Stevenson to the west – would converge on Borkardan on 24 September.

[28] At this point, Wellesley received further intelligence that, rather than being at Borkardan, the Maratha army was camped just 5 miles (8.0 km) north, but their cavalry had moved off and the infantry were about to follow.

[30] Wellesley was also eager to forge a reputation for himself, and despite his numerical disadvantage, he was confident that the Maratha's irregular forces would be swept aside by his disciplined troops, and only Scindia's regular infantry could be expected to stand and fight.

[28] Pohlmann struck camp and deployed his infantry battalions in a line facing southwards behind the steep banks of the Kailna with his cannon arrayed directly in front.

[26][34] At around 15:00, the British crossed to the northern bank of the Kaitna unopposed apart from a distant harassing fire from the Maratha cannon which was largely inaccurate but succeeded in decapitating Wellesley's dragoon orderly.

Pohlmann soon recognised Wellesley's intentions and swung his infantry and guns through 90 degrees to establish a new line spread approximately 1 mile (1.6 km) across the isthmus with their right flank on the Kaitna and the left on Assaye.

Although British artillery was brought forward to counter, it was ineffective against the mass firepower of the Maratha guns and quickly disabled through the weight of shot directed against it.

[50][51] A number of Maratha gunners who had feigned death when the British advanced over their position re-manned their guns and began to pour cannon fire into the rear of the 74th and Madras infantry.

[54] While Wellesley was preoccupied with re-taking the gun line, Pohlmann rallied his infantry and redeployed them into a semicircle with their backs to the Juah; their right flank across the river and their left in Assaye.

[57] Berar's irregulars inside Assaye, now leaderless and having witnessed the fate of the regular infantry, abandoned the village and marched off northwards at around 18:00, followed shortly afterwards by the Maratha cavalry.

[64] He remained with Wellesley to assist with the wounded – troops were still being carried from the battlefield four days after the engagement – until ordered to recommence the pursuit of the Maratha army on 26 September.

[3] Lieutenant Colonel Thomas Munro, the Company's district collector at Mysore, was critical of the high proportion of casualties and questioned Wellesley's decision not to wait for Stevenson.

[3][68] Lord Mornington and his Council lauded the battle as a "most brilliant and important victory",[69] and presented each of the Madras units and British regiments involved in the engagement with a set of honorary colours.

[71] Of the native infantry battalions, only the Madras Sappers survive in their original form in the Indian Army but they no longer celebrate Assaye as it has been declared a repugnant battle honour by the Government of India.