Ms Chornovol’s car was rammed on a road outside the capital, Kiev, late on Wednesday, and she was brutally beaten by unidentified men.
Jailed former Prime Minister Yulia Tymoshenko said she was outraged by the “atrocious cruelty” of the beating.
Two suspects were later held and police were looking for a third man.
It is the latest in a series of attacks on opposition activists.
On Tuesday, Dmytro Pylypets, who has taken part in and organised anti-government protests, was beaten and stabbed in the eastern city of Kharkiv.
Ms Chornovol has become famous for her investigative reports into the affairs of Ukraine’s top officials, whom she has accused of engaging in dubious business practices and whose wealth she has exposed.
Shortly before she was attacked, she had published a blog in which she wrote about a “country manor” which she alleged was being constructed for Interior Minister Vitaliy Zakharchenko near Kiev.
She is now in intensive care in hospital.
Last year, Ms Chornovol gained fame when she scaled the fence of a lavish country home which she alleged was owned by Ukraine’s President Viktor Yanukovych.
Pictures of the opulence of the heavily guarded house raised questions about how the president could finance such a luxurious home.
Opposition politicians condemned Wednesday’s attack on Ms Chornovol.
Leader of the opposition UDAR party Vitali Klitschko called on journalists to go on strike in solidarity with Ms Chornovol.
“They are beating journalists and trying to make them shut their mouths. They are destroying their right to a profession.
“Only cowards and moral freaks are capable of savagely beating a woman at night. Does anyone still have hopes that the authorities will change for the better and hear anyone?”, he asked in a video statement.
Ms Tymoshenko, who is in jail on what her supporters say are politically-motivated charges, said it “should be the last drop of blood and the last display of cruelty towards our people”.
Mr Yanukovych has been facing mass protests for weeks since he backtracked on a key agreement for closer ties with Europe.
Hundreds of thousands of people have regularly been taking over Kiev’s Independence Square and at times, clashed with riot police.
The leader of the far-right party Freedom, Oleh Tyahnybok, said the attack on Ms Chornovol’s life was part of a wider campaign of intimidation against the opposition.
“The terror campaign launched by the authorities continues,” he said.
President Yanukovych has ordered an investigation into the beating.
An official statement said he had “severely condemned this manifestation of violence and stressed that law enforcers must solve this case and hold those guilty accountable”.