"She breathed her last around 6 a.m. today (Sunday). Along with several veterinarians and experts from different parts of India, we made all efforts to revive her, but she passed away," Ganesh Nayak of NGO Animals Matter To Me (AMTM) told IANS.
Bijlee's body will now be taken over by the forest department and Bombay Veterinary College vets for an autopsy, he said.
A complaint has been lodged with the police in Mulund, Nayak said.
On June 11, Bijlee, 54, was found collapsed on the busy Mulund-Bhandup Link Road in eastern Mumbai, allegedly abandoned by her owners.
Nayak, along with NGO RAWW, and local volunteers Jagdish Shetty and Raju Iyer, had been taking care of Bijlee for the past 20 days.
For over a fortnight, Bijlee had been kept strapped on a crane as she could not stand or sit due to weak hind leg bones.
She was suffering from arthritis and could not walk due to a large maggot-infested wound on her hind leg.
The AMTM made arrangements to fly down vets and elephant specialists from Assam, Agra, Pune and other places to treat her.
Initially, Bijlee had responded well to the treatment, but a couple of days ago her condition suddenly deteriorated and she expired Sunday.
Moved by her plight, mega-star Amitabh Bachcan had appealed to public to help save Bijlee on social networking sites a fortnight ago.
Two other prominent organisations -- People for the Ethical Treatment of Animals (PETA) and Federation of Indian Animal Protection Organisations (FIAPO) -- separately urged the Maharashtra government to send Bijlee to a rescue centre, cancel her ownership papers and ban elephants from moving on Mumbai roads.
Bijlee had collapsed from overwork June 11. She was taken around to beg, and grace occasions like weddings and other important events. She was made to stand at the venue of such functions to salute guests.
She was forced to spend a long time standing and was hardly allowed rest, according to the volunteers who tended her.