In 1886, Cunynghame joined the
Sarawak Civil Service and served in the Rajang. In 1888, he served as Sarawak consul in
Labuan. From 1892 to 1902, he served as acting Resident of the
5th Division, Limbang, and from 1902 to 1904, Resident of the
3rd Division, Sibu. In 1895, he accompanied the Raja on an expedition against the rebels led by the Orang Kaya Tumonhhong whom they captured at Medalam. In 1903, he led a successful raid against
Dyak rebels in
Batang Lupar district for which he was complimented by the Rajah, and in 1908, led a similar expedition in the same area with
Sarawak Rangers having recently been appointed their Commandant. In 1904, he was appointed Resident of the
1st Division at
Kuching and Member of the Supreme Council. In 1906, the Rajah appointed him
officer administering the Government during his absence giving him temporary control of Sarawak. He retired from the service in 1909, and went into business becoming chairman of United Malaysian Rubber Co Ltd. During the
First World War (1914–1918) he served in the 5th Battalion,
Duke of Cambridge's Own (Middlesex Regiment), gained the rank of Lieutenant-Colonel, and was mentioned twice in
dispatches. == Personal life and death ==