He was the last Maharaja of the of Bikaner State, officially from 1950 till 1971, when the privy purse and all the royal titles were abolished by the Republic of India.

He was also a politician, serving as a member of the Lok Sabha for twenty-five years, from 1952 to 1977, and an international clay pigeon and skeet champion.

Prince Karni succeeded his father, H.H. Lieutenant-General Maharaja Sir Sadul Singh, in 1950.

In 1964 he received the degree of Doctor of Philosophy from Bombay University, for his thesis The relationship of the Bikaner royal family with central authority (1465-1949).

As well as many sports, his interests included photography and painting.

His daughter Princess Rajyashree Kumari was also a first class shooting sportswoman who received the Arjuna Award in 1968.

Karni Singh won the National Championship in Clay Pigeon Trap and Skeet seventeen times and represented India at all levels of international competition.

He was the first Indian to compete at five Olympic Games, which he did from 1960 to 1980, missing the Games of 1976.

He competed in the Asian Shooting Championships at Tokyo in 1967 and at Seoul in 1971, where he won a Gold Medal.

He won a Silver Medal at the Asian Games in Tehran, 1974, and another in the Asian Games at Kuala Lumpur in 1975.

In 1961 he was given the Arjuna award, becoming the first person from the world of shooting to be rewarded with that national honour. He documented his shooting experiences in a book of memoirs called From Rome to Moscow.

Dr. Karni Singh Shooting Range situated near the historic Tughlaqabad Fort in Delhi was named after him. It was first constructed for the 1982 Asian Games in New Delhi, and later rebuild altogether for the 2010 Commonwealth Games.

He held the following Titles:

1924-1950: Yuvaraja Sri Sadul Singh Bahadur

1950-1971: Sri Raj Rajeshwar Maharajadhiraj Narendra Maharaja Shiromani Doctor Sri Karni Singh Bahadur