Mauno Koivisto was born in 1923, the second son in the family of a ship’s carpenter. A sister was born three years later. His father had been lost to sea and had there experienced a religious awakening which was reflected in the family's life. He regarded Saturday as holy, for example - though he was not an Adventist. Mauno’s mother was the daughter of a precentor.
The tough experiences of his childhood included the death of his mother when the boy was ten and the practical household problems that began when his father was left as a single parent. After attending primary school, Koivisto had a number of jobs, and when the Winter War broke out, he joined a lire-righting unit at the age of sixteen, moving on from there to various workplaces. In the summer of 1940, during the Interim Peace, Koivisto was already keeping abreast of public issues to such an extent that he was “never terrified in the same way" as he was at that time.