Ukrainian comedian Volodymyr Zelensky will formally become the country's new president at a ceremony in the capital, Kiev tomorrow.
Mr Zelensky, who has no previous political experience, scored a landslide victory in last month's presidential election.
He ousted incumbent Petro Poroshenko who had been in power since 2014.
Mr Zelensky has promised to tackle corruption and bring an end to the war with Russian-backed rebels in the east.
It is not clear which issues he will raise in his first speech as leader. The former television actor has said little since his resounding victory on 21 April.
There has been much political wrangling over the timing of Mr Zelensky's inauguration. He had wanted to hold it today, a day of mourning for victims of Stalin-era repression in the country.
But parliament disagreed and voted to hold it tomorrow.
He made tackling Ukraine's deep-rooted corruption a major campaign theme. Last month, his aides announced plans to scrap MPs' immunity from prosecution and make military purchases more transparent.
But perhaps the biggest challenges the new leader will face is the continuing conflict with Russian-backed forces in the east.
In the run-up to his election, Mr Zelensky said he wanted to "renew relations" with eastern Ukraine and start a "powerful information war to end the conflict".
Fighting in the region has claimed about 13,000 lives since Moscow annexed Ukraine's Crimea peninsula in 2014.
There have already been indications that Russian President Vladimir Putin is determined to test the political novice.
Shortly after the election, Mr Putin made it easier for those living in eastern Ukraine's separatist territories to obtain a Russian passport. The move was widely seen as a challenge to Mr Zelensky.
In a Facebook post in response, Mr Zelensky's team labelled Russia "an aggressor state which wages war against Ukraine".
It called on the international community to provide "diplomatic pressure and the pressure of sanctions".