Siegbahn was born to Karl M. G. Siegbahn and Karin Högbom Siegbahn on April 20, 1918, in Lund, Sweden. His father was a lecturer in physics at the University of Lund and the director of the Nobel Institute for Physics of the Royal Swedish Academy of Sciences for nearly thirty years. The elder Siegbahn's discoveries and research in X-ray spectroscopy won him the 1924 Nobel Prize in physics.

The younger Siegbahn pursued his interests in mathematics, physics, and chemistry at the University of Uppsala, from which he earned his bachelor of science degree in 1939 and his master of science degree in 1942. He received his doctorate in 1944 from the University of Stockholm and worked as a researcher from 1942 to 1951 at the Nobel Institute of Physics. After a few years as a physics professor at the Royal Institute of Technology in Stockholm, Siegbahn left in 1954 to become professor and then head...