Lieutenant-General Sir Robert Arbuthnot, KCB (19 November 1773 – 6 May 1853) was a British military commander during the Napoleonic Wars.

He entered the army as a cornet in the 23rd Light Dragoons on 1 January 1797, and was present at the Battle of Ballinamuck in the Irish rebellion on 8 September of the following year.

On his return from America, Arbuthnot, then a captain in the 20th Light Dragoons, resumed his position on General Beresford's staff at Madeira, and served with him as aide-de-camp, and afterwards as military secretary, throughout the greater part of the Peninsular War.

In the same battle, at a critical moment, he was enabled by his quickness of sight to discern a retrograde movement on the part of the French, which Marshal Beresford had not perceived, and induced the latter to recall an order which he had just given for the retirement of two batteries of artillery.

At an earlier period, in South America, when he and General Beresford were prisoners in the hands of the Spanish, and when all the officers were about to be searched for papers, he contrived by a clever stratagem to secrete in an orchard an important document, viz.