In 2008, Onyango made her film debut in Wanuri Kahiu's "From a Whisper". She plays Tamani, the daughter of a businessman who learns that her long-absent mother was killed in the 1998 bombing in Nairobi, and copes by making graffiti in the memorial park. She was nominated for Best Actress in a Leading Role at the Africa Movie Academy Awards. In 2010, Onyango voiced the dragonfly in the children's TV series "Tinga Tinga Tales".