Kjellén completed gymnasium in Skara in 1880 and matriculated at Uppsala University the same year. He completed his Ph.D. in Uppsala in 1891 and was a docent there from 1890 to 1893. He also taught at Gothenburg University from 1891 and was professor of political sciences and statistics there from 1901 until he received the prestigious Skyttean professorship of Eloquence and Government in Uppsala in 1916.