He said talks might last up to 10 days.
PM Arseniy Yatseniuk`s People`s Front party could be a key partner, he added.
Pro-Western parties look set to dominate parliament after the first legislative polls since the pro-Russian former President, Viktor Yanukovych, was driven from power in February.
No votes were cast in two areas under control of pro-Russian separatists in the east of Ukraine, with 27 parliamentary seats there and in Crimea - annexed by Russia in March - remaining vacant.
Preliminary official results are expected later on Monday.
Strong mandate
However, exit polls indicated that President Poroshenko`s bloc - comprising his own Solidarity Party and Udar, led by former boxer champion Vitali Klitschko - was in the lead with about 23% of the vote.
"More than three-quarters of voters who took part in the polls gave strong and irreversible backing to Ukraine`s path to Europe," Mr Poroshenko said in televised comments.
He said that in order not to lose time, coalition consultations should start on Monday.
"We have these 10 days when we must create... the best government in Ukraine because no other government will cope with the challenges that the country is facing today," he added.
At least 3,700 people have been killed since an insurgency in the east of Ukraine began earlier this year.
Despite a truce agreed on 5 September some 300 people have been killed in sporadic clashes between the Ukrainian army and pro-Russian separatists around Donetsk`s airport.
Correspondents say that the top three performing blocs, including those of Mr Poroshenko`s and Mr Yatseniuk, are strongly pro-European and are likely to give the president a strong mandate to pursue democratic reforms and pursue efforts to end the conflict in the east.
Mr Yatseniuk`s People`s Front appeared to come second, polling in the region of 21%, while the Self Help Party, based in western Ukraine, was third with more than 13%, exit polls indicated.
But parties linked to the government of former President Yanukovych or with close ties to Russia fell behind in the parliamentary polls.
The Opposition Bloc, formed by allies of ousted Pro-Russia President Viktor Yanukovych, polled in fourth position with 8% of the vote.
Meanwhile, the pro-Russian Communist Party failed to clear 5%, the polls said, and may be without representation in parliament for the first time.
Varied turnout
The exit polls only take into account voting for 225 of the 450 seats, with results from voting for single constituency seats likely to take longer to count.
Some three million people in separatist-controlled areas in Donetsk and Luhansk were unable to vote. Leaders there say they will hold their own polls in the next month.
The election comes amid an energy crisis, with Russia cutting off gas supplies to Ukraine in June in a dispute over unpaid bills.
Ukraine`s economy is collapsing, with GDP forecast to fall between 7% and 10% this year.
Turnout reached more than 51%, according to official figures, however the turnout varied widely between the east and west of the country.
The highest percentage turnout was in the western Lviv region (about 70%), with the lowest in areas of Donetsk region under government control (about 30%).
International observers, meanwhile, expressed "serious concerns" over the effect the violence in the east of the country had on the election, with violence against candidates.
Mr Yanukovych fled in February after a wave of pro-Western protests in Kiev triggered by his refusal to sign a partnership agreement with the European Union.
Anger in eastern Ukraine at his overthrow turned to unrest with separatists seizing government buildings and beginning an insurgency in April.
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