Toni Garrn was born Antonia Garrn in Hamburg, Germany. Her father works for an oil refinery and her mother is a qualified businesswoman. She has an older brother, Niklas, who is also a model. When Garrn was two years old, she moved with her family to London, and later to Athens when she was six. By the age of 10, she moved back to Hamburg with her family.
When Garrn was 13, she was discovered by Claudia Midolo, the owner of German model agency Modelwerk during the FIFA World Cup 2006 in her hometown Hamburg, and then signed with New York agency Women Management.