Collen was born in the Marylebone district of London on 17 June 1843, the son of Henry Collen, a miniature portrait painter and early photographer to the court. He married, in 1873, Blanche Rigby, daughter of Charles Rigby, JP, and they had three sons and a daughter.
Army career
Collen joined the Royal Artillery in 1863, and served in Abyssinia in 1868 and later in Afghanistan and Sudan. After passing through Staff college in 1871-72, he joined the Indian Staff Corps. As an administrator in India, he served as Secretary in the Military Department, and was a Military Member of the Council of the Viceroy of India from December 1895 until he retired in April 1901. He was promoted to Major-General on 18 January 1900.[1]