Douglas was born in 1837, the eldest son of Sir Robert Andrews Douglas, 2nd Baronet of Douglas of Glenbervie. His grandfather, the 1st Baronet, was Kenneth Douglas, born Kenneth MacKenzie. The 3rd Baronet was educated at first in Jersey and completed his studies in Hampshire. He was gazetted into the 57th Regiment in 1854 and very quickly was on active service in the Crimean War. He was present at the storming of Sebastopol, and the capture of Kinburn, receiving the Crimean medal and clasp, and the Turkish War medal. He next served against the Arabs at Aden, and was present at the capture at Sheikothman. He then took part in the suppression of the Indian mutiny. The 57th were afterwards dispatched to New Zealand, and Sir Robert was present at various skirmishes, and at Nukumaru, receiving the honour of mention in general orders. For ten years he commanded a company of the old 'Die Hards', and the retired by sale of commission, and settled in Whangarei.