Tymoshenko is serving a 7-year prison term following a conviction on charges she abused her authority in a 2009 natural gas deal with Russian energy company Gazprom. She faces a series of other charges related to alleged economic crimes.
A united opposition composed of Tymoshenko's Fatherland Party and the People's Self-Defense Party, among others, is challenging all 450 parliamentary seats in October elections. The opposition announced it chose Tymoshenko as its leader, reports Russian news agency RIA Novosti.
Tymoshenko led the country's Orange Revolution in 2005. She staged a hunger strike early this year to protest her treatment in prison and her supporters say the charges against her are politically motivated.
The Russian report notes the nomination of Tymoshenko is largely symbolic. Ukrainian law forbids people serving time in prison from running in national elections.