Ukraine is under pressure from Western backers to defuse the conflict, which has left many people struggling to survive the frigid winter, while the cost of the fighting has pushed former Soviet republic towards the brink of bankruptcy.
A 12-point ceasefire protocol was worked out in September to end the conflict between government forces and Russian-backed separatists in which over 4,700 people have been killed.
But the truce was repeatedly flouted and Kiev made clear it would not carry out ensuing steps under the deal, including the removal of heavy artillery, until the guns fell silent.
"Today was the first night when we didn't have a single shelling, not one violation of the ceasefire regime," Poroshenko said at a part-televised meeting with security aides. "Today we face the extremely crucial task of implementing the peace plan."
Rebels disagreed with Poroshenko's assessment, accusing Kiev of further artillery bursts overnight. But his comments sounded a note of optimism ahead of a two-day visit to Kiev by the new European Union foreign policy chief, Federica Mogherini.
At a daily briefing by the Ukrainian military, spokesman Andriy Lysenko confirmed there had been no rebel attacks overnight, but said Ukrainian positions had been shelled a few times during the day on Monday.
Last week, prospects for a fresh round of peace talks between a "contact group" comprising Ukraine, Russia and the Organization for Security and Cooperation in Europe (OSCE) watchdog were dashed by renewed clashes in the east.
On Monday, senior Ukrainian presidential official Valeriy Chaliy said the contact group should meet "as soon as possible," but no date had been agreed.
Russia denies Ukrainian accusations of intervening militarily on the side of the eastern rebels. It has called for a new round of peace talks on the conflict, and on Monday urged constitutional reform by Kiev to allow more autonomy to Russian-speaking eastern areas of Ukraine.
Contradicting Poroshenko's reports of a fully-observed truce overnight, the separatist self-proclaimed Donetsk People's Republic (DNR) accused government troops of violations.
"On the night of December 15, Ukrainian punitive forces carried out artillery strikes on the territory of Donetsk airport despite the 'regime of silence'," the DNR said in an online statement.
