In the Verkhovna Rada, Ukraine's Parliament, lawmakers passed a resolution to free Tymoshenko, a hero of the country's 2004 revolution that forced the questionable results of a presidential election won by Yanukovych to be thrown out.
Tymoshenko served as prime minister from 2007 to 2010, and was forced out of office after losing an election to Yanukovych.
She was sentenced in 2011 to seven years in prison after being convicted of abuse of authority over a natural gas deal negotiated with Russia in 2009.
The case against her was widely considered to have been politically motivated, and the United States and other Western nations called her "a political prisoner."
In 2012, after she was allegedly beaten unconscious by guards, she went on a hunger strike to draw attention to "violence and lack of rights" in her country.
In Washington, White House press secretary Jay Carney said U.S. officials were closely monitoring developments. "We have consistently advocated a de-escalation of violence, constitutional change, a coalition government, and early elections, and today's developments could move us closer to that goal," he said in a statement.
Russia's ambassador to the United Nations, Vitaly Churkin, condemned what he called Western attempts to influence the outcome of the tumult in Ukraine.
"Either they don't understand the consequences of what they're doing, or they're engaged in a very provocative game of destabilizing Ukraine and therefore Eastern Europe," Churkin said in a post on his official Twitter account.
A day earlier, Churkin accused the opposition of wanting to take power by force.
"If those so-called democratic opposition leaders come to power on the shoulders of thugs that will not produce democracy in Ukraine," he said.
By Saturday, a tidal wave of political change appeared to be engulfing Ukraine with key Yanukovych allies leaving office, and the presidential duties being handed off until a new cabinet has been selected.
During the parliamentary session, resignations were announced for the speaker and another leading presidential ally.
Hours later, Parliament elected a new speaker, a rival to Yanukovych, and gave him the duty of coordinating the executive office until a new cabinet is in place.
Another opposition parliamentarian received the duties of acting interior minister.
The Verkhovna Rada sacked Yanukovych's prosecutor general.
The unrest began in November, when Yanukovych scrapped a European Union trade deal and turned toward Russia.
Russia, which has offered to lend money to cash-strapped Ukraine in a deal worth billions of dollars and to lower its gas prices, has pressured Yanukovych to crack down on demonstrators.
Western leaders, who have offered Ukraine a long-term aid package requiring economic modernization, urged him to show restraint, open the government to the opposition and let the democratic process work out deep-seated political differences.
But the fight was also about corruption and control. The opposition called Yanukovych heavy-handed, with protesters saying they wouldn't leave Independence Square until he resigned.
Tensions boiled over Tuesday, when security forces charged into a Kiev crowd with stun grenades, nightsticks and armored personnel carriers. The violence escalated, leaving dozens -- protesters and police alike -- dead.