"I intend to run for president of Ukraine," the 53-year-old told reporters after gingerly walking into a press room with the help of a walking stick she uses due to chronic back pain.
The brief but dramatic announcement encapsulates the spectacular changes that have swept the economically struggling and culturally splintered ex-Soviet state of 46 million in the past few weeks.
Tymoshenko -- one of the most charismatic and outspoken leaders of Ukraine's 2004 pro-democracy Orange Revolution -- lost a close presidential poll to Yanukovych in 2010 after heading two pro-Western cabinets that became embroiled in internal disputes and eventually lost popular support.
Yanukovych's government quickly launched a series of criminal probes against his political rival that led to a controversial trial over Tymoshenko's role in agreeing a 2009 gas contract with Russia that many Ukrainians thought came at too high a price.
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Tymoshenko was convicted in October 2011 for abuse of power and sentenced to a seven-year jail term that Western nations denounced as politically motivated.
But she emerged triumphantly from the state hospital in which she had spent most of her sentence under guard on February 22 -- the day parliament ousted Yanukovych for his role in the deaths of nearly 100 protesters in Kiev earlier that month.
The crowd's reception of the one-time opposition icon was guarded. Many remained wary of the ugly corruption allegations that have stained Tymoshenko's reputation.
Tymoshenko today attempted to paint herself as a compromise figure who could look after the interests of her old supporters while reassuring Russian speakers, particularly in Ukraine's southeast, who have traditionally relied on the Kremlin for support.
"I will be able to find a common language with everyone who lives in the east," Tymoshenko said before adding that she still viewed Russian President Vladimir Putin as "Ukraine's enemy number one".