He was born in Komotini and entered the Hellenic Military Academy in 1970, graduating in 1974 first of his class and being named a Second Lieutenant of Infantry.

Frangos commanded the 32nd Marines Brigade in 2002–2003, before being assigned to head the Hellenic National Defence General Staff's Planning Directorate.

In 2004 he was promoted to major general and assumed command of the Inter-service Military Intelligence Directorate.

[1] On 6 August 2009, by decision of the Government Council for Foreign Affairs and Defence, he was appointed Chief of the Hellenic Army General Staff,[1] a position he held until a surprise major reshuffle in the Greek military leadership on 1 November 2011.

On 17 May 2012 he was named as Minister for National Defence in the caretaker cabinet of Panagiotis Pikrammenos, which led the country until the June general election.