Konstantinos Mitsotakis was born on October 18th, 1918 in the district of Halepa, Chania, Crete. He's the second son of Kyriakos Mitsotakis and Stavroula Ploumidaki and comes from a family with a long political tradition.
His grandfather, Costis Mitsotakis (1845-1898), bridegroom of Eleftherios Venizelos, was the founder of the "Party of the Barefeet", which was later received by Eleftherios Venizelos and renamed to "Liberal Party". The old-Costis Mitsotakis, husband of Katigo (nee Venizelos), was one of the most important personalities of the time and for about thirty years had a leading role in all political and armed struggles of Crete. After his death in 1898, the Greek government honored him by voting in Parliament a law on the awarding of honorary pension to his widow and orphan children.
His father, Kyriakos Mitsotakis (1883-1944), in 1905 was the Secretary General of the Movement of Therissos Assembly and between 1915 -1920 he was congressman of Chania. During the Balkan War of 1912, leading a body of Cretan volunteers fought in Macedonia and Epirus, playing a leading part in the liberation of Siatista. Additionally, during the German occupation, he participated in the resistance as a political member of the National Organization of Crete (NOC).
His father's brother, Aristomenis Mitsotakis (1884-1941), was also a congressman of Chania, in 1924 he served as Minister of the Economy in the Papanastasiou Government and also Vice President of the Parliament. He led the movement that occurred in Chania, Crete in the summer of 1938, against the Metaxas regime, after the failure of which fled to Cyprus where he died in exile in 1941.
On the mother's side, his grandfather Harry Ploumidakis (1866-1943), Eleftherios Venizelos's first cousin, was the first Christian mayor of Chania, later was elected to the Cretan Parliament in 1891 while, he served as Interior minister during the Cretan State period.
Konstantinos Mitsotakis studied Law and Political and Economic Sciences at the University of Athens, from where he graduated with honors shortly before the start of the Greek-Italian war in 1940. The costs of his studies were covered by endowment of Eleftherios Venizelos.
Konstantinos Mitsotakis married Marika Yannoukou in 1953, with which he had four children: Dora, Alexandra, Katerina and Kyriakos.