In terms of his overseas and campaign service, William Parlby served with his regiment in India and then as a colonel he commanded other regiments in India e.g. the 10th (The Prince of Wale's Own) Royal Regiment of Light Dragoons (Hussars) based in Kirkee, India. In 1854 after the disastrous Charge of the Light Brigade he was ordered to bring his regiment (then the 10th Hussars) from India to the Crimea (via Egypt), the 680 strong regiment arrived on 15 April 1855 to join Allied troops laying siege to the city of Sebastopol. During the latter stages of the Crimea War he commanded the British Cavalry Division from 17 April to 30 June 1855 and then the Cavalry Division's Hussar Brigade from 1 July to 2 September 1855. He was also present with Turkish forces at the Battle of the Chernaya. He was thoroughly involved in cavalry operations around Sevastopol and Lord Raglan complimented him in despatches. He was awarded the Crimea Medal with Clasp for Sebastopol, the Sardinian and Turkish Crimea Medals and 4th Class Order of the Medjidie.