[2] Ioannidis was born in Athens to a wealthy, upper middle-class business family (although he claimed to come from poverty) with roots in Epirus.

[6] Ioannidis took an active part in planning and executing the coup d'état of 21 April 1967 (he was Director of the Hellenic Military Academy), but despite his great power he preferred to stay in the shadows, allowing George Papadopoulos to take the limelight.

Ioannidis proceeded to install his friend Phaedon Gizikis as figurehead President of Greece, although total power belonged to him.

He did not control the higher military hierarchy completely, but he could impose his will on them with the support of the lower ranks nicknamed "the small junta" (Ta Paraskinia tis Allagis-Stavros Psicharis-1975).

While in power, Ioannidis would regularly place conditions on all discussions with the U.S. embassy as noted by then ambassador Henry Tasca, despite maintaining publicly support for NATO due to his anti-communist stance.

[6] When he did not manage to appoint the President of the Supreme Court and an ex-minister Zenon Severis, he tried to show to the outside world that the coup was merely an internal affair, but this effort went without any success.

Ioannidis could not survive such a humiliation, and was pushed out by the "coup of the generals" in August, headed by then Prime Minister Konstantinos Karamanlis, ending seven years of military rule.

[4][21] On 14 January 1975, Ioannidis was detained and tried on charges of high treason, rebellion, and of being an accessory to the manslaughters perpetrated during the Athens Polytechnic uprising.