Sadiq al-Madhi died from the novel coronavirus, his moderate Islamist National Umma party said on Thursday while offering condolences to the Sudanese people.
Madhi was transferred to the United Arab Emirates for treatment three weeks ago after being hospitalized in Sudan and testing positive for the virus.
On Friday, the government declared three days of national mourning for the former premier.
He was a staunch opposition figure during Bashir’s long rule and threw his weight behind a mass protest movement that eventually prompted the military to overthrow the president last year.
Mahdi was toppled in 1989 by now-ousted president Omar al-Bashir in an Islamist-backed military coup.
Sudan has recorded nearly 17,000 coronavirus cases including more than 1,200 deaths.