Reports suggest that Singh is in critical condition.
The 76-year-old leader fell down at his residence at around 11pm on Thursday, following which he was rushed to the hospital.
Jaswant Singh's background
Singh was expelled from the BJP before Lok Sabha poll after he decided to contest the general elections from Barmer in Rajasthan as an Independent candidate. Though, he had lost the elections.
Singh who served as Minister of Finance, Defence and External Affairs in the Union Cabinet left the Army in 1966 to join politics. In 1967, he unsuccessfully contested his first election as an Independent candidate. In the following years, he got in touch with senior Jan Sangh leaders Bhairon Singh Shekhawat and Atal Bihari Vajpayee. Singh got his first victory in 1980 when he was elected to the Rajya Sabha.
Singh became Finance Minister in the Atal Bihari Vajpayee Cabinet in 1996. He then served as External Affairs Minister in the Vajpayee Government from December 5, 1998 to July 1, 2002.
It was during this period relations with Pakistan hit a low patch and terrorist hijacked Indian Airlines flight.
He was also the Deputy Chairman of the Planning Commission in 1998. His last major position was as Leader of Opposition in the Rajya Sabha from 2004 to 2009.
Singh's flip-flop with BJP
In August 2009, he was expelled from BJP following criticism over his remarks in his book, 'Jinnah: India-Partition-Independence' which allegedly praised the founder of Pakistan.
But a year later, in 2010, he was re-inducted into the party.
In March, 2014, he was denied a ticket by the party to contest the 2014 Lok Sabha elections from the Barmer-Jaisalmer constituency in Rajasthan. Subsequently, he was expelled from the party after he refused to withdraw his nomination as an Independent candidate. He lost the election to BJP's Sonaram Choudhary.