Tzitzikostas studied politics and diplomacy at Georgetown University and worked at the office of the Chair of the United States House Committee on Foreign Affairs.

In 2001 he created his own company selling organic dairy products called 'MACEDONIAN FARM', which was later marketed by Mevgal.

Since 2015, he has been a member of the European Committee of the Regions, and in July 2017, he was elected Head of the Greek Delegation.

In February 2020, he was unanimously elected by all political groups President of the European Committee of the Regions.

In August 2024 the Greek government nominated Tzitzikostas as the country’s European Commissioner in the von der Leyen Commission II.