Comedian Volodymyr Zelensky announced a snap parliamentary election during his swearing-in as Ukraine's new president.
The election was expected to take place in October 2019. But at the ceremony in Kiev Mr Zelensky said "I am dissolving the Verkhovna Rada (parliament)".
He said ending the conflict with Russian-backed rebels in the east would be his top priority.
A political novice, he campaigned strongly against official corruption.
"People must come to power who will serve the public," he said on Monday.
Russian President Vladimir Putin said he would not congratulate Mr Zelensky on his inauguration, but would wait for "the first successes in settling the internal conflict in south-eastern Ukraine, and in normalising Russian-Ukrainian relations".
Meanwhile, Russia's Foreign Minister Sergei Lavrov called on Ukraine's new leader to implement the Minsk peace accord agreed in 2015, and also suggested an "all for all" prisoner swap between both sides.
Mr Zelensky a former television star, acted the part of Ukrainian president in a popular comedy series. He scored a landslide victory in last month's presidential election.
"We must become Icelanders in football, Israelis in defending our native land, Japanese in technology," he said at the swearing-in.
He said Ukrainians must also "become Swiss in our ability to live happily with each other, despite any differences".
"Our first task is to achieve a ceasefire in Donbas," he said, referring to the eastern region controlled by Russian-backed rebels.