Lieut.-Colonel Reynell resigned the appointment of deputy quartermaster-general in India, and was brought on full pay as major of the ninety-sixth regiment on the 5th May 1808, and on the 22d of September following was appointed major in the SEVENTY-FIRST regiment. In October 1808, Brevet Lieut.-Colonel Reynell embarked as military secretary to Lieut.-General Sir John Cradock, who had been appointed to command the forces in Portugal, and landed in November at Lisbon. He remained in Portugal until April 1809, when Sir John Cradock was superseded in the command of the forces in Portugal by Lieut.-General Sir Arthur Wellesley. Lieut.-Colonel Reynell afterwards accompanied Lieut.-General Sir John Cradock to Cadiz, Seville, and Gibraltar, of which latter place Sir John Cradock was appointed governor, and Lieut.-Colonel Reynell remained there as military secretary until September, when he returned to England. Lieut.-Colonel Reynell joined the SEVENTY-FIRST regiment at Brabourne-Lees Barracks in December 1809, immediately after its return from Walcheren. In September 1810 he embarked at Deal with six companies of the SEVENTY-FIRST regiment for Portugal, landed at Lisbon towards the end of that month, marched soon after to Mafra, and thence to Sobral, where the six companies joined the army under Lieut.-General Viscount Wellington. In October Lieut.-Colonel Reynell had the honor of being particularly mentioned by Viscount Wellington in his despatch, containing an account of the repulse of the attack of the French at Sobral on the 14th of that month. The British army shortly afterwards retired to the lines of Torres Vedras, and Brevet Lieut.-Colonel Reynell was appointed assistant adjutant-general to the fourth division under Major-General the Honorable George Lowry Cole. Early in March 1811, the army of Marshal Massena broke up from its entrenched position at Santarem, and retreated to the northward. Brevet Lieut.-Colonel Reynell entered Santarem with the fourth division the day after Marshal Massena had left it, and continued in the pursuit of the French army to the Mondego. In the affair of Redinha he had a horse killed under him. From Espinhal the fourth division was ordered to retrograde, and recross the Tagus, for the purpose of reinforcing Marshal Sir William Carr Beresford. In 1811 he joined the Marshal at Portalegre, and being the senior British assistant adjutant-general, was directed to join Marshal Beresford’s head-quarters, and proceeded with him to Campo Mayor, from which the enemy retired; was also present at the capture of Olivença, and subsequently accompanied the marshal to Zafra, between which place and Llerena a smart skirmish occurred with the enemy’s hussars. In May 1811, Lieut.-Colonel Reynell returned to England from Lisbon with despatches from Viscount Wellington.