Instantly recognisable for her elaborate braided blond hair, the 53-year-old shot to fame with her impassioned speeches against a rigged poll won by the now deposed pro-Russian Viktor Yanukovich in 2004.
Her ringing rhetoric electrified thousands with Yanukovich forced out and herself propelled to power.
With the post-Soviet establishment turfed out, Tymoshenko served as prime minister in 2005 and 2007-2010, under ally president Viktor Yushchenko, who was famously left disfigured after being poisoned during the 2004 election.
Ousted after a returning Yanukovich beat her to the presidency in 2010, she was jailed in 2011 over a gas deal she signed with Russia. She spent much of her incarceration in hospital for a back problem in the north-eastern city of Kharkiv.
The West said her imprisonment was politically motivated, and the EU repeatedly pressed for her release, only to be rebuffed by Yanukovich.
Tymoshenko is reported to have made millions in the 1990s as president of a company that was for a while the main importer of Russian natural gas, earning her the sobriquet “Gas Princess”.
Her sharp tongue and combative style brought her both devout followers and enemies.
Born in 1960, in Russian-speaking Dnipropetrovsk in eastern Ukraine, Tymoshenko studied at the local university. She married while still a teenage student to Oleksandr, who now sells medical equipment to hospitals, and has one 34-year-old daughter, Yevgenia, who was schooled in Britain and attended university at the London School of Economics.
Taking advantage of an entrepreneurial climate in the Soviet Union under leader Mikhail Gorbachev, Tymoshenko had her first taste of self-made money from a video rental store she set up. She soon crossed into the energy sector and went on to become head of Unified Energy Systems.
Tymoshenko entered parliament in 1996 and was made deputy prime minister in 2000.
She fell victim, however, to political intrigues under president Leonid Kuchma and spent several weeks in jail on corruption charges. She was cleared.
On leaving prison, she changed her image, lightening and braiding her hair and wearing sharply tailored, folk-inspired designer outfits.
Her stylist told media that the look was designed to distance herself from an association with wealth and to emphasise a national Ukrainian identity.
She is now immediately catapulted to the forefront of Ukrainian politics, but will find the stage more crowded than before, with a new generation of revolutionaries including former world heavyweight boxing champion Vitali Klitschko, who led the mass protests that appear to have brought down Yanukovich.