Scoop, best known for the hit tracks "Be Faithful" and "It Takes Scoop," collapsed on stage at Hamden Town Center Park, Connecticut and was taken to hospital where doctors were unable to revive him, US media reported.
Medical staff apparently attempted to administer CPR while he was still on the stage, according to a video of the incident obtained by celebrity news site TMZ. He was then carried away on a stretcher.
"It is with the heaviest of hearts I announce the passing of Isaac Freeman III, known professionally as Fatman Scoop," manager Birch Michael wrote on Facebook.
"You taught me how to be the man I am today. I love you Scoop. Thank you so much for everything you gave to me," Michael added.
Hip-hop star Missy Elliott led the tributes to Scoop, writing on X that Scoop's "voice and energy have contributed to many songs that made the people feel happy and want to dance for over two decades. Your impact is huge and will be never be forgotten."
Radio host Shelley Wade posted a photograph of herself with Scoop, writing: "We are losing too many of our #HipHop legends too soon. Rest easy, Scoop."
Scoop briefly became embroiled in a political row in Australia in 2018 when the country's then-prime minister Scott Morrison posted a clip that featured his hit "Be Faithful."
Morrison, a conservative evangelical Christian, deleted the post after his critics said the entertainer's lyrics were inappropriate and unparliamentary.
"It's quite clear that that is not a song on my playlist," he later told reporters in Sydney.
The uproar prompted a response from Scoop, who tagged Morrison in an Instagram post saying: "I am humbled to have my voice rocking in the highest offices of the Australian Government!"
The rapper defended his lyrics: "It's a fun PARTY SONG that has no NEGATIVITY or HARM in it!!" before extending Morrison a backstage invite to a festival appearance in Australia.
