"I will do everything possible not to let down and justify the trust in me of the party's council," the businessman and former national Security Council secretary said.
The party's press service said earlier that two other nominees - acting Prime Minister Yuriy Yekhanurov and the head of Our Ukraine's political committee, Roman Bezsmertniy - had withdrawn their candidacies.
Bezsmertniy said earlier three pro-Western groups - Our Ukraine, the bloc of former prime minister Yulia Tymoshenko, and the Socialist Party - had clinched a deal to form a majority coalition in Ukraine's parliament. He said Tymoshenko would be appointed prime minister. But a Tymoshenko bloc spokesperson was cautious about the deal, saying it had to be signed ahead of a Friday deadline after which President Viktor Yushchenko could dissolve parliament and call fresh elections.
Poroshenko, one of President Viktor Yushchenko's closest associates and Ukraine's richest men, owns a number of food industry enterprises and headed the Ukrainian National Security Council in February-August 2005.
He added that Our Ukraine had recommended that the other two parties sign the coalition agreement.
"We decided [at the meeting] that we approve the agreement on the formation of the 'orange' coalition and ask the deputies elected from Our Ukraine bloc to sign the agreement," he said.