Roman Zvarych, an ally of Yushchenko, chaired the session saying that 227 signatures appeared on the document - with a majority of 226 members required to win most votes in the chamber.
The coalition deal followed weeks of negotiations between the two "orange" groups, which set aside differences during their election campaigns to win the slender majority.
Yushchenko came to power after mass protests against electoral fraud in 2004, which became known as the "Orange Revolution", but the movement could not maintain its unity.
Tymoshenko became the first prime minister of Yushchenko's presidency, but he dismissed her after seven months amid mutual allegations of corruption.
Since the "Orange Revolution", Ukrainian politics have seen a power struggle between Yushchenko and Viktor Yanukovych, who was his bitter rival in the 2004 presidential vote that sparked the demonstrations.
Yanukovych lost to Yushchenko in a court-ordered rerun of the elections, but he rebounded in 2006 when his Party of the Regions, got the largest share of votes in parliamentary elections and he became prime minister.
Yushchenko has accused Yanukovych this year of attempting an illegal power-grab and called new elections, which were held in September.
Together, the parties of Yushchenko and Tymoshenko received more votes than Yanukovych's party, and after reaching a majority coalition in parliament on Thursday, they now have 30 days within which to form a cabinet.