Singh, who was with the Samajwadi Party for a large part of his political career, was once considered one of the most powerful politicians in Uttar Pradesh and New Delhi.
Union minister Nitin Gadkari said in a tweet that he felt very sad to hear the news of the demise of Amar Singh.
That Amar Singh was highly driven is a trait acknowledged by Prime Minister Narendra Modi who in his tweet recalled him as an energetic public figure who witnessed some of the major political developments from close quarters and known for friendship across many spheres of life.
Kalraj Mishra, another senior BJP leader, expressed grief on Amar Singh's death.
He is survived by his wife Pankaja and twin daughters.
A couple of hours prior to his demise, Singh had paid tribute to freedom fighter Lokmanya Tilak in a tweet. Singh and his protege, actor Jaya Prada, were expelled from the Samajwadi Party in February 2010 for "anti-party activities".
In 2016, he was elected to the Rajya Sabha with support from Samajwadi Party.
A flamboyant politician who often did not pay much heed to demands of political correctness in his interactions, including with the media, Amar Singh shot into the league of top politicians as Mulayam Singh Yadav's close aide.
Venkaiah Naidu to Madhya Pradesh Chief Minister Shivraj Singh Chauhan condolences poured in as the news broke. "Om Shanti." While many people have been mourning Singh's demise, his former close friend Amitabh Bachchan, who is now hospitalised for his COVID 19 treatment, also shared a gloomy post after the news of the veteran politician's death surfaced.
Amar Singh was the general secretary of the Samajwadi Party and a member of the Rajya Sabha. "No matter which party he belonged to, he had good relations with everybody". But that was not the first time that he had been expelled from the party.