Shakeel Ahmed Sheikh, a former aide of underworld kingpin Dawood Ibrahim, breathed his last at Jaslok Hospital here on Monday.
Sheikh alias Lambu Shakeel, was suffering from heart disease and had been admitted to the hospital for a few days.
According to reports, Sheikh was one of the key accused in a criminal conspiracy to smuggle explosives into India and conduct blasts at the behest of Dawood Ibrahim.
Dawood Ibrahim, who heads the D-Company, a Mumbai-based organised crime syndicate, is responsible for the 1993 Mumbai blasts which left 257 people dead and hundreds injured, after 13 blasts rocked the country's financial capital.
The underworld don, who lives in Pakistan, is designated as a global terrorist and is wanted in India for several crimes including murder, extortion, targeted killing, drug trafficking and terrorism.