In October last year, Swamy was arrested and charged under the country's anti-terrorism laws, which critics have described as draconian.

In the incident, known as the Bhima Koregaon case, bloody clashes broke out between lower-caste and other regional groups in the state of Maharashtra.

Hundreds of thousands of Dalits -- who are ranked the lowest in India's caste-based system -- had gathered in the village of Bhima Koregaon to mark the 200th anniversary of a battle in which they, as part of the then-British colonial army, defeated an upper-caste ruler, when the violence broke out.

Authorities accused Swamy of having ties with the organization responsible for the violence, and allege that he had links to Maoist rebels, who are considered one of the country's biggest security threats. In a video recorded days before his arrest, Swamy denied all involvement and said he had never visited the location where the violence took place.

His arrest sparked outrage worldwide, prompting several opposition politicians, national and international rights groups to demand his release.

'Prefer to die in jail'

Despite Swamy's worsening health, which was exacerbated when he contracted coronavirus in prison last month, authorities repeatedly rejected his lawyers' pre-trial bail pleas to allow him to recover at home.

The National Investigation Agency in-charge of the case had contested Swamy's bail application on medical grounds, citing the severity of the accusations against him, and claimed he was receiving proper care within the prison.

The activist told the court he would "prefer to die in jail, rather than get admitted to any hospital," according to court documents reviewed by CNN.

On court orders, Swamy was moved to the Holy Family Hospital at the end of May.

In light of Swarmy's ailing health, he was allowed medical treatment at a private hospital, where since May 28 he had received "all possible medical attention," the ministry said.

A slew of opposition politicians, rights groups and academics, have expressed sadness for his death -- as well as anger for the laws under which he was arrested and denied bail. Critics have long accused India's government of increasingly using anti-terrorism laws as a means to quell any form of dissent.

In a statement Monday, the Archbishop of Bombay, Oswald Cardinal Gracias, called Swamy's arrest "very painful."

"One is innocent until proved guilty," the statement said. "Fr. Stan's case did not even come up for hearing."

Gracias added Swamy had given marginalized groups in India a "sense of dignity and upliftment," adding that he worked "single-mindedly for the poor."

Harsh Mander, a prominent Indian rights activist called Swamy's death a "tragedy for the nation."

Meenakshi Ganguly, South Asia director of Human Rights Watch, said Swamy's arrest highlights "a degree of cruelty and callousness that is shameful."

"The counter terror law is draconian. We see it is being used rampantly to jail peaceful critics without bail," Ganguly said. "It was for the courts to decide if Swamy was guilty, but in repeatedly stifling bail, the authorities chose not to protect," the "fragile, ailing" activist, she added.