Sir Salman Rushdie is on a ventilator and unable to speak after being stabbed on stage in the US, his agent says.
Andrew Wylie said that the author, 75, may lose one eye after the attack at an event in New York state.
Sir Salman went into hiding with police protection in the UK in 1988 after Iran's top leader called for his murder over his novel, The Satanic Verses, which some Muslims deemed blasphemous.
Police detained a suspect named as Hadi Matar, 24, from Fairview, New Jersey.
New York State Police said the suspect ran onto the stage and attacked Sir Salman and an interviewer at the Chautauqua Institution in western New York state.
Sir Salman was stabbed at least once in the neck and in the abdomen, authorities said. He was taken to a hospital in Erie, Pennsylvania, by helicopter.
"Salman will likely lose one eye; the nerves in his arm were severed; and his liver was stabbed and damaged," his agent said.
No motive or charges have yet been confirmed by police, who are in the process of obtaining search warrants to examine a backpack and electronic devices found at the centre.
Police told a news conference that staff and audience members had pinned the attacker to the ground where he was arrested. A doctor in the audience gave Sir Salman first aid.
The interviewer who was with Sir Salman, Henry Reese, suffered a minor head injury and was taken to a local hospital. Mr Reese is the co-founder of a non-profit organisation that provides sanctuary to writers exiled under threat of persecution.
Linda Abrams, an onlooker from the city of Buffalo, told The New York Times that the assailant kept trying to attack Sir Salman after he was restrained.
"It took like five men to pull him away and he was still stabbing," Ms Abrams said. "He was just furious, furious. Like intensely strong and just fast."
India-born novelist Sir Salman catapulted to fame with Midnight's Children in 1981, which went on to sell over one million copies in the UK alone.
But his fourth book, published in 1988 - The Satanic Verses - forced him into hiding for nearly 10 years.
The surrealist, post-modern novel sparked outrage among some Muslims, who considered its content to be blasphemous - insulting to a religion or god - and was banned in some countries.
Several people were killed in anti-Rushdie riots in India and in Iran the British embassy in the capital, Tehran, was stoned.
In 1991 a Japanese translator of the book was stabbed to death, while a few months later, an Italian translator was also stabbed and the book's Norwegian publisher, William Nygaard, was shot - but both survived.
A year after the book's release, Iran's Supreme Leader Ayatollah Khomeini called for Sir Salman's execution. He offered a $3m (£2.5m) reward in a fatwa - a legal decree issued by an Islamic religious leader.
The bounty over Sir Salman's head remains active, and although Iran's government has distanced itself from Khomeini's decree, a quasi-official Iranian religious foundation added a further $500,000 to the reward in 2012.
There has been no reaction from the Iranian government to Sir Salman's stabbing. Iranian media were describing Sir Salman as an apostate - someone who has abandoned or denied his faith - in their coverage.
The British-American citizen - who was born to non-practising Muslims and is an atheist himself - has become a vocal advocate for freedom of expression, defending his work on several occasions.
Sir Salman Rushdie has faced death threats for more than 30 years since the publication of The Satanic Verses. Sir Salman said the main thrust of his novel was to examine the immigrant experience, but some Muslims were offended by portrayals of the Prophet Muhammad and the questioning of the nature of the revelation of the Quran as the word of God.
The Satanic Verses was banned first in the author's country of birth, India, and then several other countries before Iran's Ayatollah Khomeini issued his infamous fatwa.
The fatwa called for the killing of anyone involved in the publication of the book and offered rewards to those who took part in the murders. That fatwa has never formally been rescinded.
Surprised by the widespread nature of the protests, Sir Salman apologised to Muslims but went into hiding.
When Sir Salman was knighted in 2007 by the Queen, it sparked protests in Iran and Pakistan, where one cabinet minister said the honour "justifies suicide attacks".
Several literary events attended by Sir Salman have been subject to threats and boycotts - but he continues to write. His next novel, Victory City, is due to be published in February 2023.
Fellow authors such as JK Rowling and Stephen King have written messages of support.
Booker-prize winning author, Ian McEwan, called it an "appalling attack" that "represents an assault on freedom of thought and speech"
"Salman has been an inspirational defender of persecuted writers and journalists across the world. He is a fiery and generous spirit, a man of immense talent and courage and he will not be deterred," he added.
Writer Taslima Nasreen, who was forced to flee her home in Bangladesh after a court said her novel Lajja offended the Islamic faith, said she now feared for her own safety in the wake of Sir Salman's attack.