Mantila graduated in 1995 from the University of Art and Design in Helsinki after studying screenwriting and directing for five years. She wrote and directed radio dramas and stories and wrote the novel Varpunen, published in 2005. She had directed several short films before making her feature film debut Neitoperho (The Collector, 1997). Afterwards she made Pelon maantiede (The Geography of Fear, 2000) for which she won the Jussi award (Finnish national film award) for the screenplay. She worked on a couple of TV series (Yhteinen huone, 2000 and Täysin työkykyinen, 2002), and afterwards made her latest feature film Ystäväni Henry (My Friend Henry, 2004).