Announcement to contest elections expected in May comes as IMF says it will provide loans worth up to $18bn to country.
Ukrainian former prime minister Yulia Tymoshenko, released from jail last month after President Viktor Yanukovich was forced by protesters to leave power, has announced she will run again for president in an election slated for May 25.
"I plan to run for election as president" and stand "a candidate for Ukrainian unity," Tymoshenko told reporters on Thursday.
Tymoshenko, 53, served twice as prime minister and ran for president in 2010, only to be narrowly beaten in a run-off vote by Yanukovich.
Yanukovich subsequently launched a campaign against Tymoshenko and her allies, and she was jailed in 2011 for abuse of office linked to a gas deal she brokered with Russia in 2009.
The announcement came as the International Monetary Fund pledged up to $18bn in loans on Thursday to prop up Ukraine's sinking economy.
Arseniy Yatsenyuk, Ukraine's interim prime minister, has forecast more pain ahead without reforms that will affect nearly everyone in the country.
In a lengthy and passionate address to parliament, Yatsenyuk warned that Ukraine was "on the brink of the economic and financial bankruptcy" and laid out details for fixes needed to put the country back on track, including raising taxes, a freeze on minimum wage and radically higher energy prices.
The reforms will hit households hard, which is likely to severely dent the interim government's tenuous hold on power.
"We have no choice but to tell Ukraine the truth," Yatsenyuk said.
Ukraine is still battling to restore some semblance of normalcy since Yanukovich was ousted after months of protests ignited by a decision to back away from closer relations to the EU and move towars Russia.
In fast-moving events since Yanulovish's ousting, Moscow has annexed Ukraine's Crimean peninsula, which last week voted to become part of the Russian Federation.
The IMF said on Thursday that recent economic policies had drastically slowed growth and brought foreign currency reserves to a "critically low level."
In a statement issued after two weeks of talks with officials in the Ukrainian capital, Kiev, the IMF said loans could range between $14bn and $18bn.
It said a more exact sum would only be determined, however, when authorities give a more precise assessment of their needs.
Other donors, including the European Union and Japan, have already pledged further assistance to Ukraine, conditional on the conclusion of an IMF bailout and reform package.
The total amount of assistance available for Ukraine will be about $27 billion over the next two years.