[1][2] He is first mentioned in 1057, the year his elder brother Isaac I Komnenos, at the head of a group of generals, rebelled against Michael VI (r. 1056–1057) and forced him off the throne.

At the time of the revolt, John held the post of doux, but after his brother's victory, he was raised to the rank of kouropalates and appointed as Domestic of the Schools of the West.

[5][6] The crown then passed to Constantine X Doukas (r. 1059–1067), although Bryennios asserts that it was first offered to John, who refused it, despite the pressure of his wife, Anna Dalassene, to accept.

[7] According to the historian Konstantinos Varzos, however, this version is suspect, and may well be a post-fact attempt at legitimizing the eventual usurpation of the throne by John's son, Alexios I Komnenos (r. 1081–1118).

[8] John is not mentioned in the sources during the reign of Constantine X, perhaps indicating, according to Konstantinos Varzos, that he was in imperial disfavour, despite Bryennios' assertion that both he and his brother remained much honoured by the new emperor.