In that year he was appointed aide-de-camp to General Fox-Strangways, who commanded the artillery in the Crimea; but, on his way out from England, he learned that Strangways had been killed in the battle of Inkerman.
He received a brevet majority on 2 November 1855, the Légion d'honneur of France, and the fifth class of the Medjidie, and was created a companion of the Order of the Bath.
Reilly became regimental lieutenant-colonel in 1868, and next year was the guest of Lord Mayo in India, whence he wrote some descriptive letters to The Times newspaper.
He spoke French fluently, and at the end of October 1870, while the siege of Paris was going on, he was sent out as extra military attaché to the British embassy at Tours.
In recognition of his services the French government raised him to the grade of officer of the Legion of Honour on 20 March 1872, and commander on 4 November 1878.
In January 1879 he was appointed to command the royal artillery at Aldershot, but in the following month he was sent out to South Africa, in a similar capacity, to take part in the Zulu War, which was then entering on its second stage.
The energy that underlay his normal composure was conspicuously shown in the last months of his life, when he vindicated the ordnance department from the charges formulated by Colonel Hope in the columns of the Times.
A commission on warlike stores was appointed, under the chairmanship of Sir James Fitzjames Stephen to investigate the allegations; its report supported the charge of weak administration, but refuted that of corruption.