During a visit to Washington DC, the president told a joint meeting of the Senate and House of Representatives that his forces need more political support throughout the world.
"They need more military equipment, both lethal and non-lethal, urgently," he said, asking for aid going beyond equipment such as night-vision goggles that Washington has already sent.
"Blankets, night-vision goggles are also important, but one cannot win the war with blankets," he said.
Poronshenko also called for more sanctions against Russia, who Ukraine and NATO accuses of backing the rebels in the five-month conflict in eastern Ukraine that the UN says havs killed more than 2,700 people.
He called Russia's annexation of Crimea one of the most "cynical acts of treachery in modern history".
His emotional speech was interrupted frequently by applause and standing ovations, Al Jazeera reported.
"I also asked that the United States be forceful and reflect its principles with the respect of further sanctions against the aggressor," Poroshenko said.
The White House did announce a new $46m security package for Ukraine's military that includes counter-mortar radar to detect incoming artillery fire, but stopped short of the request for lethal aid.
The US will also provide vehicles and patrol boats, body armour and heavy engineering equipment, while also giving $7m to humanitarian organisations to assist people affected by the violence.
The US has so far provided about $60m in nonlethal aid to Ukraine's military.