Siegbahn was born in Örebro, Sweden, and his parents was Georg Siegbahn and Emma Zetterberg. He graduated in Stockholm 1906 and begun his studies at Lund University the same year. During his education he was amanuensis for Johannes Rydberg. In 1908 he studied at the University of Göttingen. He obtained his Ph.D. at the Lund University in 1911, his thesis was titled Magnetische Feldmessungen (magnetic field measurements). He became acting professor for Rydberg when his health was failing, and succeeded him as full professor in 1920. However, in 1922 he left Lund for a professorship at the Uppsala University.