Gurmeet Ram Rahim Singh, 50, is due to appear at a court in Panchkula, Haryana state, on Friday to hear the verdict in a case involving the rape of two women.
Parts of Punjab and Haryana have been placed in lockdown and mobile internet services suspended in some areas.
Thousands of police and paramilitary forces have been deployed.
The high court in the state has asked the government to use force, if necessary, to control the crowds.
Ram Rahim Singh denies the allegations, which date back to 2002.
The chief of the Dera Sacha Sauda sect dresses up in colourful clothes, with a rock star image.
He has published half a dozen music videos and regularly performs at rock concerts, which are attended by tens of thousands of followers.
The Dera Sacha Sauda website says it is a "social welfare and spiritual organisation that preaches and practices humanitarianism and selfless services to others".
The sect claims to have more than 50 million followers around the world and says it campaigns against female foeticide, for reforms for sex workers, runs schools and several hospitals.
In recent months, the Dera chief has been mired in controversy, amid allegations that he forced 400 followers to undergo castrations so that they could get "closer to god". He also faces trial for murder, charges a spokesman for the sect has denied.
He has been opposed by mainstream Sikh leaders, who accuse him of insulting and belittling their faith.
The crowds in Panchkula, where the court will deliver its verdict, have sparked a massive security deployment across the city.
Schools and offices in the area were closed, trains were halted, roads were blocked and three stadiums were set aside as makeshift prisons in case of trouble, officials said.
As many as 200,000 devotees of the highly influential guru have gathered, many desperate to get a glimpse of Singh as he heads into the court.
Authorities are concerned and are preparing for a possible public backlash from his supporters.
Ram Rahim Singh, who has repeatedly denied any wrongdoing in the long-running case, is one of India's most powerful gurus, with a god-like status.
He wields considerable political influence and claims to have tens of millions of followers worldwide.
Ram Rahim Singh is described by devotees on numerous websites as a saint as well as an author, inventor, scientist, philosopher, philanthropist, peace activist and "the ultimate humanitarian".