Hedberg was ordained 1834 and became curate in Siuntio, then in Lohja, belonging since 1836 to Pietist revivalist movement led by Savonian farmer and lay preacher Paavo Ruotsalainen. Soon Hedberg became one of the leaders of this movement in southern Finland. Rationalist diocesan chapter begun to dislike Hedberg's activity because of his Pietism and he was transferred first to Paimio 1838 and 1840 as prison chaplain in Oulu. 1842 he became temporary curate in distant Raippaluoto and 1843 curate in Pöytyä.
Later years Hedberg focused more and more on sacraments and on mystical union with Christ. In St Andrew's church in Kimito the Eucharist was celebrated every Sunday during Hedberg's time, which was at that time very rare. As celebrant he also always used chasuble.
W.A. Schmidt, Fredrik Gabriel Hedberg. Helsinki 1951
Esa Santakari, Vanhan Hedbergin sakramenttimystiikka. Elevatis Oculis, studia mystica in honorem Seppo A. Teinonen. Annals of the Finnish Society for Missiology and Ecumenics, 42, 1984. ISBN 951-95206-7-8