He joined the East India Company on 14April 1849. He was posted in the 1st
Madras fusiliers as a second lieutenant in September 1850. After seeing action in the
Second Anglo-Burmese War at Pegu (now known as
Bago, Myanmar) in December 1852 and again in January 1853, he became an assistant commissioner in Tenasserim (now known as the
Tanintharyi Region) and was severely wounded in 1856-57 while fighting insurgent Karens and Shans in the Yunzalin District. He then moved back to mainland India and joined in the recapture of
Lucknow from Indian soldiers in March 1858. He also took part in the Oudh campaign with Sir
James Hope Grant and Sir
Alfred Hastings Horsford. In 1866, he went to
Mandalay as agent of the chief commissioner, and in August of that year had a narrow escape from a body of insurgents who had murdered three of the royal princes. During the disturbances that ensued he embarked nearly all the Europeans and other Christians at the Burmese capital on board a river steamer and brought them safely to
Rangoon, for which he received the thanks of the governor-general. The insurrection having been put down, he returned to Mandalay. In May 1867, he exerted his influence with the king to prevent the execution of three young princes, two of whom owed their lives to his intercession, the other having been beheaded before a reprieve arrived. Shortly afterwards he obtained the king's assent to a new treaty of commerce and extradition which was ratified by the governor-general on 26 November 1867. From 1876 to 1885, Sladen was commissioner of the
Arakan division and in the latter year he accompanied the force sent against
King Thibaw, as chief political officer. In this capacity, on the arrival of the British troops at Mandalay, on 28 December 1885, he entered the royal palace, and received the king's submission. In a speech on 17 February 1886, the governor-general,
Lord Dufferin, made special mention of ‘Colonel Sladen, to whose courage and knowledge of the people we are so much indebted for the surrender of the king’. ==Personal life==