The 2004 protests brought her and fellow Orange leader Viktor Yushchenko to power. But once in government, their alliance rapidly fell apart.
Mr Yushchenko, as president, sacked her from the office of prime minister in 2005, as she feuded with his party colleagues.
Now Ms Tymoshenko is back as PM, with the narrowest majority in parliament.
Her party resurrected its alliance with President Yushchenko for elections in September 2007 and she insists the coalition will stand firm in a parliament noted for feuding and double-dealing.
Critics accuse Ms Tymoshenko of being unpredictable and opportunistic, while her supporters see her as a glamorous revolutionary challenging a corrupt, macho political elite.
Her powers of oratory inspired the huge crowds in Kiev in November-December 2004 and helped sweep Mr Yushchenko to power in the Orange Revolution.
Supporters of the revolution will now be asking if she can deliver the promised economic revival put on hold by months of political deadlock.
Campaign for reform
Her stinging attacks on the oligarchs who prospered under the former administration of Leonid Kuchma boosted her popularity among many Ukrainians frustrated by years of economic stagnation and corruption.
But critics point to her controversial past - it is widely reported that she made a fortune in the energy sector in the 1990s.
Ms Tymoshenko castigated the government for its gas deal with Russia in January 2006, agreed hastily after Russia's state-owned energy giant Gazprom suspended supplies to Ukraine over Kiev's refusal to accept a four-fold price rise.
The deal gave Rosukrenergo - a joint venture between Gazprom and an Austrian investment firm, Centragas - a virtual monopoly over Ukraine's gas imports.
Ms Tymoshenko's frustration with Russia came to the surface when she cancelled her first official trip to Moscow, after Russia's state prosecutor had warned that she was on a wanted list for alleged fraud dating back to the 1990s.
"I think everyone remembers how certain Russian bureaucrats used to work against the Ukrainian opposition, I think it is hard to drop old habits," she told the BBC.
Russia had also campaigned openly for Mr Yushchenko's arch-rival in the 2004 presidential election - Viktor Yanukovych.
Commenting on the Orange Revolution's triumph over Leonid Kuchma's protege, she said "the monsters who had kept Ukraine in a criminal state left the stage".
Such comments make it unlikely that she will join any government led by Mr Yanukovych, whose party now forms a powerful opposition, with the largest single number of votes polled in the election.
Distinctive style
Ms Tymoshenko, 45, was born in the industrial city of Dnipropetrovsk, in the mainly Russian-speaking east, which is now a stronghold of Mr Yanukovych.
She trained as an engineer and economist in the east and pushed through energy sector reforms in Mr Yushchenko's government in 1999-2001.
Last October her daughter Yevhenia, 25, married a British rock singer, Sean Carr. They met during the Orange Revolution.
"He is a nice person and he adores my daughter, that's the most important thing," the new mother-in-law said.
Yulia Tymoshenko takes pride in her own distinctive style, which has been copied by models around the world.
"I just heard the latest joke about my hair: 'Do you know what that is on her head? It's a steering wheel to drive the state'," she told the BBC's Sarah Rainsford.
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