 Feldt was the son of a single mother, Irma, née Jonsson, who had to send young Kjell-Olof to live with his grandfather's sister because of his father's alcoholic problems.Though he came from a working-class family, Kjell-Olof managed to gain admission to Uppsala University where he received a Politices Magister (MA in political science) degree in 1956.He received a Licentiate degree at Lund University in 1967.