Savchenko was arrested in March 2018 on charges of planning to attack parliament with hand grenades and automatic weapons. She rejected the charges as an attempt by President Petro Poroshenko to get rid of a powerful challenger.
Savchenko became a national hero in Ukraine after spending years in a Russian prison. She was freed in 2016 under international pressure, but after returning home to a hero's welcome quickly fell out with Poroshenko, accusing his government of corruption and incompetence.
Poroshenko is trailing comedian Volodymyr Zelenskiy ahead of Sunday's runoff.