She played Tatiana Romanova in the BBC Radio 4 adaptation of Ian Fleming's 1955 James Bond novel From Russia, With Love opposite Toby Stephens as Bond. The play was narrated and directed by Martin Jarvis.

Fedori finished high school in Ukraine, and continued her education at the Donetsk National University, studying International Relations and Law to become a diplomat; however, after her freshmen year, she did a student exchange program in Kansas, at Neosho County Community College along with other 13 top Ukrainian freshmen. Remarkably, she was able to advance from NCCC to Harvard. Fedori graduated from Harvard University with BA Cum Laude and won the 'Caroline Isenberg Acting Award' in 2004. she began her professional acting career in off-broadway theater in NYC and Boston, working with Jay Scheib, whom she met working on a show Lorenzaccio at the American Repertory Theater, while still at Harvard. In addition to being an Actress, Olga also had fronted a band, ICIA, in London, 2006-2008.

Fedori appeared in The Adventure of Earthboy and Stargirl in the title role as Stargirl in 2006. In 2007, she appeared in British television shows Skins, in which she played Anka in the sixth episode and EastEnders, playing Anya Covalenco.

She appeared as the leading female character Scarlett in the short film Birdfeeder which premiered in Brighton on 2 May 2007.

On 21 June 2008 at the Edinburgh International Film Festival, her first feature Mum & Dad, in which she plays the lead–protagonist Lena, premiered at the Filmhouse.

She first appeared in the BBC One medical drama Holby City on 12 May 2010, portraying the character of Frieda Petrenko, a Ukrainian nurse and later Doctor (Fedori had to emphasise her Ukrainian accent for the part), and was shortlisted for the "Best Newcomer" award at the 2011 National Television Awards for the role. She left the series on 15 May 2012, returning on 12 December 2017.