The retired sportsman, 42, had initially announced plans to run for the office of president in February (14) following the ousting of leader Viktor Yanukovych, who went into hiding after violent riots erupted on the streets of the nation's capital, Kiev.
Klitschko stepped down from the race in March (14) and instead threw his support behind billionaire chocolate maker Petro Poroshenko, who became a presidential favourite to beat ex-Prime Minister Yulia Tymoshenko at the polls, while he decided to run for the position of Mayor of Kiev.
Ukrainians voted for their new leaders on Sunday (25May14) and both Poroshenko and Klitschko emerged victorious.
Celebrating the news with fans on Twitter.com, Panettiere, who is engaged to wed Klitschko's brother Wladimir, writes, "#Ukraine finally gets the leaders it deserves! Congratulations to my brother and the new Mayor of #Kiev #VitaliKlitschko!!"
Filmmaker Wes Craven also sent his well wishes to the boxer-turned-politician, tweeting: "Congrats to the new mayor of Kiev - #VitaliKlitschko".