Mariniki has studied journalism and French literature at the Athens University. She has freelanced for major Greek newspapers, radio and television networks and magazines. Until 2010, she worked as a staff journalist for Lambrakis Press S.A., writing for To Vima daily newspaper and Vimagazino, the weekly supplement of To Vima newspaper.
Her work focuses primarily on social issues, leading her to cover big news events like the 2007 fires in Peloponnese, the 2008 Athens riots, as well as immigration issues. She has travelled extensively, covering major news events around the globe, such as the earthquake in Haiti, the reality on the ground for the Palestinian people in Gaza after the bloodshed caused by the Israeli army on the flotilla which tried to break the embargo in 2010, and the mudslides that devastated Uganda during the same year. Today, she works as a journalist for E, the weekly supplement of Eleftherotypia newspaper, and as a freelancer for various other publications.