Captain Reynell was afterwards appointed aide-de-camp to Major-General Cradock, who was ordered to proceed from Egypt with a force of four thousand men to Corfu; but while at sea counter-orders were received, and he proceeded to Malta, and subsequently to England. In July 1804 he embarked as aide-de-camp to Lieut.-General Sir John Cradock, K.B., who had been appointed to the command of the troops at Madras, and while on the passage, namely, the 3d of August 1804, he was promoted to the rank of major in the fortieth regiment.
On the 10th of March 1805 Major Reynell received the brevet rank of lieut.-colonel, upon being appointed deputy quartermaster-general to the King’s troops in the East Indies. In July following he was appointed aide-de-camp to the Marquis Cornwallis, governor-general of India, and accompanied his lordship from Madras to Bengal, with whom he remained until his lordship’s decease, at Ghazepore, in October 1805. Lieut.-Colonel Reynell returned to Madras immediately afterwards, and was appointed military secretary to the Lieut.-General Sir John Cradock, the commander-in-chief at that presidency. He officiated during several months of the year 1806 as deputy adjutant-general in India, in which country he remained until October 1807, when he returned with Lieut.-General Sir John Cradock to Europe, and arrived in England in April 1808.
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 He remained in Portugal until April 1809, when Sir John Cradock was superseded in the command of the forces in Portugal by Lieut.-General Sir Arthur Wellesley.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.