Kostas graduated in first place from the Oinousses Marine Academy in 1995. He was honoured by the Foundation of Pateras and the Leon Lemos Charitable Foundation as well as Anangel Shipping Enterprises (in memory of Antonios Angelicoussis), being the top graduate in his year out of the nine marine captains' academies in Greece.

Kostas served in the Greek Merchant Navy as a Deck Officer up to and including the rank of Chief Officer for six years on a wide variety of vessel types. He also worked for a period of five years as a cargo and nautical surveyor as well as claims handler in a Piraeus based Claims & Average Agency, and two years in a Greek law firm dealing mainly with casualties and cargo matters. He also spent four months working in Tsakos Shipping (London) Ltd., the Insurance & Claims Dept. of Tsakos Group. Kostas holds an OPITO approved HUET certificate for offshore helicopter operations.