He was admitted to the Singapore hospital eight months ago. He is survived by wife Pankaja and twin daughters.
The apogee of his career and its denouement was the 2008 trust vote faced by the Manmohan Singh-led UPA I government after its Left Front allies pulled out support over the Indo-U.S. nuclear deal. "In the last few decades, he witnessed some of the major political developments from close quarters". Although he was mostly with the SP, but he made friends across the spectrum of political parties.
"Amar Singh Ji was an energetic public figure", Modi wrote.
"We are deeply sorry at the passing away of Rajya Sabha MP Shri #AmarSingh". From Vice President Venkaiah Naidu to Madhya Pradesh Chief Minister Shivraj Singh Chouhan condoled as news broke.
Kalraj Mishra, another senior BJP leader, expressed grief on Amar Singh's death.
Earlier in the day, the former SP leader had posted messages on Twitter, paying tributes to Bal Gangadhar Tilak on his 100th death anniversary and also wishing people on Eid.
His media interactions organised mostly outside his Lodhi Estate official residence in the national capital would draw media persons in drove for his outspoken attacks on his rivals, which sometime included Mulayam Singh Yadav and the Bachchan family after he had a fallout with them. Many believed that Yadav liked Singh for his cross-party and industry links, and go-getter attitude that helped his party navigate demands of realpolitik. He was once considered SP founder Mulayam Singh's close confidante. But Mr Singh had denied it. But that was not the first time that he had been expelled from the party. But as Akhilesh Yadav got control of the party, he was expelled again in 2017.
He was subsequently elected as a member of parliament in India's Rajya Sabha by voters in Uttar Pradesh. Ambani, however, later resigned in 2006. The only party leader to walk away with him was actress and MP Jaya Prada to whom he had been a mentor in her political career. She, however, lost to her bete noire Azam Khan.
In February this year, Mr Singh had apologised to Amitabh Bachchan for "overreaction" against the superstar.
Singh had been suffering from kidney ailments for a long time and had undergone a transplant in 2009 and again in 2018.