Renzi said the two men at the centre of Europe's worst security crisis in years would meet at 8:00 am (1030 IST) on the sidelines of a summit of Asian and European leaders (ASEM).
The talks will also be attended by German Chancellor Angela Merkel, French President Francois Hollande, Britain's Prime Minister David Cameron and other senior officials, Renzi said.
Renzi said a statement would be made to the press on the outcome of the talks. The Italian premier, who is hosting the ASEM summit as Rome currently holds the European Union's rotating presidency, will meet Poroshenko tomorrow evening and hold further talks with Putin on Friday afternoon.
Friday's meeting comes against a backdrop of a ceasefire in eastern Ukraine between government forces and pro-Moscow rebels, which has generally held despite numerous breaches.