At the age of eight, his father was deposed and Pratap Singh became the Maharaja.

He was educated at the Royal Military Academy, Sandhurst and at Badingham College in Surrey.

After formally succeeding to the gadi in 1941, Pratap Singh was commissioned a Lieutenant in the British Indian Army and served in the Second World War.

Following Independence, he served as aide-de-camp to the President of India, as well as the head of the Sikh Regiment.

On 15 August 1947, Pratap Singh signed the Instrument of Accession to the Dominion of India and merged Nabha into PEPSU in 1948, from which point his rule ended.