Boris, the eldest surviving son of Emperor Peter I of Bulgaria and Maria (renamed Eirene) Lekapena, a granddaughter of Emperor Romanos I Lekapenos of Constantinople, had been born by 931, when he had visited Constantinople together with his mother.

Nothing else is known of Boris II's life until 968, when he went to Constantinople again to negotiate a peace settlement with Emperor Nikephoros II Phokas, and apparently to serve as an honorary hostage.

This arrangement had been intended to put an end to the conflict between Bulgaria and Constantinople, who would now join forces against Prince Sviatoslav I of Kiev, whom the Greek emperor had pitted against the Bulgarians.

In 969, when a new Kievan invasion defeats the Bulgarians again, Peter I abdicates to become a monk.

In circumstances that are not entirely clear, Boris II is allowed to return to Bulgaria and sit on his father's throne.

(The later Byzantine chronicle of John Skylitzes confounds this with a later event, in which Boris and his brother escaped Constantinople after the so-called rebellion of the Kometopouloi in Macedonia.)