Konstantinos V. Diakonis was born in Rhodes on December 18, 1978. In 1997, he was admitted to the Law School of Democritus University of Thrace through the Panhellenic Examinations, from which he graduated in 2002.

In 2004, he was admitted, after entrance exams, to the postgraduate department of the Criminal and Criminological Sciences sector at Democritus University of Thrace, from which he graduated in 2006, earning a Master’s Degree in "Criminal and Criminological Sciences" with an "Excellent" grade of 9. His thesis, titled "Res Judicata in Criminal Trials (the identity of the narrowly defined object of a criminal trial as a fundamental condition for the creation of res judicata)," remains unpublished to date.

In 2006, he was further accepted as a Ph.D. candidate by Professor (Prof. Dr. Dres. hc) Ulfrid Neumann at Johann Wolfgang Goethe University in Frankfurt, where he was awarded the title of Doctor of Criminal Law with the grade "Magna cum Laude" (With High Honors). He authored a dissertation titled “Die Geringfuegigkeitsvorschriften der StPO als Teil der Problematik der Kollision zwischen primaeren und sekundaeren Prinzipien des Rechts” (The Provisions on Insignificance in the German Code of Criminal Procedure as Part of the Problem of Conflict between Primary and Secondary Legal Principles), which was published in Germany.

Konstantinos V. Diakonis is a lawyer at the Court of Cassation (Areios Pagos) and has been a member of the Hellenic Criminal Law Association since 2006. In practice, Konstantinos Diakonis has participated as defense counsel or legal representative of the prosecution in some of the most significant criminal cases that have affected the society of the Dodecanese. These include intentional homicide cases, where he successfully secured the release of an accused from pre-trial detention, as well as felony-level financial crimes, such as the banking scandal in Karpathos. He has also handled cases involving the formation of criminal organizations, drug trafficking, human trafficking, pimping, rape, smuggling of illegal immigrants, felony fraud, embezzlement, and usury, achieving remarkable successes. He was one of the few lawyers to successfully annul a European Arrest Warrant. Additionally, he has made a significant appearance before the Supreme Court of Greece (Areios Pagos) in criminal cases, with notable success rates in appeals that he undertook, drafted, and defended.

In 2022, he was appointed Honorary Consul of the Federal Republic of Germany for the region of Rhodes and the Dodecanese in general.