Zelensky’s sudden rise comes at a time voters around the world have turned the status quo upside down, putting anti-establishment forces such as Donald Trump and Italy’s 5-Star Movement into power.
His victory reflected voters’ frustration with politics as usual.
Just nine percent of Ukrainians trust their national government, the lowest of any electorate in the world, a Galluppoll in March showed.
If polls are correct, he will be elected for a five-year term.
Mr Zelensky spoke to his supporters after the election on Sunday: “I will never let you down. I am not yet officially the president.
“But as a citizen of Ukraine I can say to all countries in the post-Soviet Union: Look at us. Anything is possible!”
With no prior political experience, the 41-year-old told Reuters in an interview in February that ‘this is a new face’ as he pointed to his face.
He explained: “I have not deceived people. They identify with me because I am open, I get hurt, I get angry, I get upset. I do not hide my emotions on camera, I do not try to look different.
“If I’m inexperienced in something I’m inexperienced. If I don’t know something, I honestly admit it.”
He announced his bid for the presidency on New Year’s Eve, upstaging Poroshenko who was giving a traditional televised address to the nation.
His campaign relied heavily on quirky social media posts to his millions of online followers, jokey posters, comedy gigs and winking allusions to the fictional president he portrays on screen.
Meanwhile Poroshenko admitted defeat and would be leaving office next month, but said he firmly stressed ‘I will not quit politics’
He later tweeted: “A new inexperienced Ukrainian president…could be quickly return to Russia’s orbit of influence.”
Critics question Zelensky’s political inexperience and he remains something of an unknown quantity for investors who want reassurances that he will accelerate reforms and keep Ukraine in an International Monetary Fund programme.
As his campaign gathered steam, Zelensky brought reform-minded former ministers to his team as advisers, providing a measure of reassurance to investors who nevertheless found his answers on policy questions vague at times.
Zelensky told Reuters he would not allow Ukraine to default on its debt commitments to the IMF, which has propped up the economy with billions of dollars in loan.
He hopes the country will eventually stop relying on the IMF but, for now, he would not allow Ukraine “to default and spoil the image of our country”.
Asked for his position on whether he would allow household gas prices to rise to market levels, another IMF demand, Zelensky was short on specifics.
He said Ukraine’s tariffs were the lowest in Europe but still too high for many.