Oles Buzyna, 45, was killed by shots fired from a car, Interior Ministry adviser Anton Herashchenko said.
Mr Buzyna is the latest in a series of allies of Ukraine's pro-Russian former President, Victor Yanukovych, to die in suspicious circumstances.
His killing comes a day after MP Oleg Kalashnikov, who was close to Mr Yanukovych, was shot dead in Kiev.
Mr Herashchenko said he believed both killings were related to the victims' involvement with Ukraine's "anti-Maidan" movement, which opposed the popular overthrow of Mr Yanukovych in 2014.
According to Mr Herashchenko, both men were key witnesses in a criminal case related to pro-Russian activists who attacked protesters in the Maidan Square uprising that deposed Mr Yanukovych.
Mr Buzyna, who was an active blogger and briefly editor of pro-Russian daily newspaper Segodnya, was killed outside his home.
Ukrainian President Petro Poroshenko has ordered an investigation into the murders, calling them "deliberate" acts that play "into the hands of our enemies".
At least eight other officials connected to Mr Yanukovych's government have died suddenly in the past three months.
Authorities initially labelled some of the deaths suicides, but later they said it was possible that some of the people were killed or forced to take their lives.
Asked about the shooting of Mr Buzyna on a call-in programme, Russian President Vladimir Putin said: "This is not the first assassination. There is a whole series of such killings in Ukraine."
Image courtesy of Wikimedia Commons user .
A Ukrainian journalist known for his pro-Russian views has been shot dead in the capital Kiev.