Jakac was born in Novo Mesto, which was then part of Austria-Hungary. He started painting in 1910 or 1911, when he was attending the Novo Mesto grammar school, and more seriously, when he was attending the technical high school in Idrija, which he finished in 1917. As he lacked money to continue the studies, he had to set off to the Isonzo Front to fight for the monarchy. In 1918, after World War I ended, Ivan Vavpotič, his former professor, introduced him to the prominent Slovene Impressionist painter Rihard Jakopič, who exhibited Jakac's paintings and became his first true tutor.