He is best known for his actions during the Partition of India, when he assisted the locals of the Gilgit Agency and led a coup d'état, codenamed Operation Datta Khel, against Hari Singh, the Maharaja of the erstwhile princely state of Jammu and Kashmir.

His father William Brown had served with the Gordon Highlanders regiment of the British Army during World War I, and was a recipient of the Military Cross.

[4] Following his arrival in India, Brown attended the Officer Cadet Training Unit in Bangalore, and was commissioned as a Second Lieutenant into the 10th/12th Frontier Force Regiment.

[6] As Pakistani militias closed in on the capital of Srinagar by 26 October, Hari Singh had fled from the princely state and signed an instrument of accession for Jammu and Kashmir with India.

The decision by the Maharaja—a Hindu Dogra ruler governing a princely state with a Muslim-majority populace—to accede to a Hindu-majority India following the creation of Pakistan was seen as controversial.

[11][12] Brown then requested for troops to be sent to the Gilgit Agency from Pakistan and established a de facto military administration on 1 November.

On assuming direct control of the region, Brown thwarted plans by a large section of his contingent to set up an independent republic called Gilgit−Astor.

[13][14] He was then instructed by Sir George Cunningham, the then-Governor of the North West Frontier Province to restore order in the region.