In 1975 he was sent to Pakistan and given the name Nabi Ahmed Shakir. He was successful in getting admission in Karachi University and completed his LLB. He joined Pakistan Army and became a commissioned officer and later was promoted to the rank of a Major. He converted to Islam, married a local girl Amanat, and became father of a son who also died on 2012-2013.From 1979 to 1983, while in military service, he passed on valuable information to RAW which was of great help to the Indian defence forces.He was given the title of 'Black Tiger' by India's then home minister S.B. Chavan.Some testify that the title was conferred by then Prime Minister, Indira Gandhi.He spent 26 years of his life away from his home and family in Pakistan in very unfavourable conditions.In September 1983, Indian intelligence agencies had sent an agent, Inyat Masiha, to get in touch with Black Tiger. But the agent was caught by Pakistan’s intelligence agencies and revealed Ravinder Kaushik's true identity.
Kaushik was then captured, tortured for two years at an interrogation centre in Sialkot. Ravinder was awarded death sentence in the year 1985. His sentence was later commuted to a life term by the Pakistan Supreme court.Kaushik was kept in various jails, including Sialkot, Kot Lakhpat and in Mianwali jail for 16 years, where he contracted Asthma and TB. He managed to secretly send letters to his family in India, which revealed his poor health condition and the trauma faced by him in Pakistani jails.
In one of his letters he wrote,
"Kya Bharat jaise bade desh ke liye kurbani dene waalon ko yahi milta hai?" (Is this the reward a person gets for sacrificing his life for a great nation like India?)
On 21 November 2001, he succumbed to pulmonary tuberculosis and heart disease in New Central Jail Multan. He was buried behind that jail.