Isle of Wight. His great-great-grandfather, Sir Walter Walker, of Bushey Hall, Hertfordshire, was advocate to Catherine of Braganza [q. v.], the wife of Charles II.
By Queen Charlotte's desire, he received a commission as ensign in the 95th foot on 4 March 1782. He became lieutenant on 13 March 1783, and on 22 June was transferred to the 71st, the 95th being disbanded. The 71st was also disbanded soon afterwards, and on 15 March 1784 he was transferred to the 36th. He joined that regiment in India, and served with General (afterwards Sir Henry) Cosby's force in the operations against the Poligars in the neighbourhood of Tinnevelli in February 1786, being placed in charge of the quartermaster-general's department. He was invalided home in 1787, and exchanged on 25 July to the 35th foot. In 1788 he was employed on the staff in Ireland as aide-de-camp to General Bruce. On 13 March 1789 he was made captain-lieutenant in the 14th foot, but, instead of joining that regiment in Jamaica, he obtained leave to go to Germany to study tactics and German.
On 4 May 1791 Walker obtained a company in the 60th, all the battalions of which were in America; but he seems to have remained at the depôt, and in 1793 he went to Flanders with a body of recruits who had volunteered for active service. He was present at the action of 10 May 1794 near Tournay, and served in the quartermaster-general's department during the retreat of the Duke of York's army, being employed on various missions. When the army embarked for England he was made an inspector of foreign corps, and was sent to the Black Forest and Switzerland to superintend the raising of Baron de Roll's regiment. He made arrangements for the passage of the men through Italy and their embarkation at Civita Vecchia, and returned to England in August 1796.
Walker was promoted major in the 60th on 27 Aug. In March 1797 he went to Portugal, and was aide-de-camp first to General Simon Fraser (d. 1777) [q. v.], and afterwards to the Prince of Waldeck, who commanded the Anglo-Portuguese army; but ill-health obliged him to go home in June. He was inspecting field-officer of recruiting at Manchester from February 1798 till March 1799. He then joined the 50th in Portugal, having become lieutenant-colonel in that regiment on 6 Sept. 1798; but in October he was summoned to Holland to act as British commissioner with the Russian troops under the Duke of York. He afterwards accompanied them to the Channel Islands, and so missed the campaign in Egypt, in which his regiment had a share. He took over the command of the 50th at Malta in October 1801, returned with it to Ireland in 1802, and served with it in the expedition to Copenhagen in 1807, being in Spencer's brigade of Baird's division.
In January 1808 he went with it to the Peninsula, as part of Spencer's force. It was one of the regiments particularly mentioned by Sir Arthur Wellesley in his report of the battle of Vimiero. It formed part of Fane's brigade, which, with Anstruther's brigade and Robe's guns, occupied a hill in front of Vimiero, and was attacked by a strong column under Laborde. The French had nearly reached the guns when Walker wheeled his right wing round to the left by companies, poured a volley into the flank of the column, charged it both in front and flank, and drove it in confusion down the hillside (see Fyler, pp. 105–7, where his own account of the charge is quoted).
In the autumn he went to England, and the 50th was commanded by Major (afterwards Sir Charles James) Napier during Moore's campaign. He returned with despatches for Moore, but reached Coruña two days after the battle. He was made colonel in the army on 25 Sept. 1808. In 1809 he served in the Walcheren expedition, at first in command of his regiment, and afterwards as brigadier.
In August 1810 he went back to the Peninsula with the rank of brigadier-general. He was employed for a year in the north of Spain, aiding and stimulating the authorities of Gallicia and the Asturias to raise troops and take a more active part in the war (see his letters to Lord Liverpool in War Office Original Correspondence, No. 142, at Public Record Office). He had persuaded Lord Liverpool to let him take three thousand British troops to Santona, but Lord Wellesley interposed, and the men were sent to Wellington (Despatches, Suppl. Ser. vii. 268). Finding that he could do no good with the Spaniards, and having become major-general on 4 June 1811, he applied to join the army in Portugal, and in October he was given command of a brigade in the 5th (Leith's) division.
At the storming of Badajoz, on the night of 6 April 1812, Walker's brigade was ordered to make a false attack on the San Vincente bastion, to be turned into a real attack if circumstances should prove favourable. The ladder party missed its way and delayed this attack for an hour. Meanwhile the breaches, which were on the opposite side of the fortress, had been assaulted in vain by the fourth and light division; and the third
