Adityanath, 49, rose from humble beginnings to become head priest of an important Hindu temple and founded a vigilante youth group.
Its volunteers regularly rough up Muslims and low-caste Dalits accused of slaughtering cows – sacred to Hindus – or of seeking to seduce women from India's majority religion.
After coming to power in Uttar Pradesh in 2017, his administration brought in a law to ban "love jihad" – Muslims marrying Hindus to convert them – and has targeted journalists and others with what critics call spurious "sedition" charges.
Media reports say more than 100 alleged criminals – most of them Muslims or Dalits – have been victims of extra-judicial police killings, a charge Adityanath denies.
And his government is widely seen as having bungled its response to COVID-19, including by concealing the real death toll.
But he won his own seat in Gorakhpur with more than 66 per cent of the vote.
Michael Kugelman of the Wilson Center tweeted that Adityanath "may be the biggest winner" from the polls.
"The BJP's performance in UP will likely strengthen his case within the party brass to be viewed as the eventual successor to Narendra Modi," he added.
Congress's humiliation in Punjab further erodes the claim of the Gandhi dynasty's once-mighty party to be the only national alternative to the BJP.
The victor in Punjab, the AAP, already runs the capital New Delhi and hopes to supplant Congress as the second-biggest party in other upcoming state elections.
"This revolution first happened in Delhi, now it has happened in Punjab and next it will happen in the rest of the country," AAP head and Delhi Chief Minister Arvind Kejriwal said.