Sikorski was born in Tuszów Narodowy, Galicia, at the time part of the Austro-Hungarian Empire. He was the third child in his family; his father was Tomasz Sikorski, a school teacher; his mother was Emilia Habrowska. His grandfather, Tomasz Kopaszyna Sikorski, had fought and been wounded at the Battle of Olszynka Grochowska in the November Uprising, during which he received the Virtuti Militari medal.