Tablighi Jamaat leader Muhammad Saad Khandalvi has been charged with manslaughter after a meeting the organisation held in Delhi spawned Covid-19 clusters across India.
Police say the gathering, which began on 3 March, was not ended even when India announced a lockdown on 24 March.
The event has been linked to 1,023 cases across 17 states – believed to be spread by infected foreign attendees.
Mr Saad and the Tablighi Jamaat have denied any wrongdoing.
The Delhi police said that Mr Saad had been charged with culpable homicide not amounting to murder, which means he will not be able to apply for bail.
The charges were brought against him while he was in self-isolation.
Police say he ignored two notices to end the event at a mosque in Delhi’s Nizamuddin area.
However, the organisation says they had suspended the event and asked everyone to leave as soon as Prime Minister Narendra Modi announced that there would be a day-long national curfew on 22 March.
While many were able to leave, they say, others were stranded because states began to seal their borders the following day, and two days later, India went into lockdown, suspending buses and trains.
The mosque’s premises include dormitories that can house hundreds of people.
The organisers say they informed the local police about all of this and continued to co-operate with medical officers who came to inspect the premises.