Papahelas was born in Athens in 1961 the son of Aristomenis and Aikaterini Papahelas. The family's origins lie in Messinia, southern Peloponnese and in Istanbul. Papahelas grew up in the Athens district Plateia Victorias. He attended Athens College and then went to the United States for tertiary studies. He majored in economics and history at Bard College and later received a Master's in Journalism and International Relations from Columbia University.
Papahelas started his journalistic career in 1983, as the New York City correspondent for the daily Greek newspaper I Avgi, then for Kathimerini, the BBC Greek service and Mega Channel. He returned to Greece in 1998 and wrote for the newspaper To Vima as well as co-hosting, with Pavlos Tsimas and Tasos Telloglou, the news program "Mavro Kouti " ("The Black Box") on Mega Channel for two years. In 2000, he launched the current affairs program "Oi Fakeloi " ("The Files") on Mega Channel which continued for seven years. He was also director of the news desk at Mega as well as the channel's political commentator.
In September 2006, Papahelas began writing for Kathimerini and in April 2007 became the newspaper's editor in chief. In October 2007, Papahelas began the news program "Oi Neoi Fakeloi" ("The New Folders") on Skai TV with Tasos Telloglou and Sofia Papaioannou.
Papahelas has interviewed nearly all the important political figures in modern Greece along with various international figures, among them the military commander of the Zapatista movement, Subcomandante Marcos, in his jungle headquarters in Mexico, Yasser Arafat in his headquarters in Ramallah, former UN Secretary General Kofi Atta Annan, Microsoft Chairman Bill Gates, US Presidents Bill Clinton and George W. Bush, and financier George Soros.
Papahelas is the creator of a pioneering series of history documentaries, including one on the 1922 destruction of Smyrna with rare interviews and footage, the 1967-74 dictatorship in Greece, the 1974Turkish invasion of Cyprus, the issue of Missing Cypriots. He has interviewed many prominent Greeks such as the politician Leonidas Kyrkos and former king Constantine.
In his first book, entitled “The rape of Greek democracy,” Papahelas documented evidence of the relation between the CIA and the Greek colonels’ group behind the junta. The cover of the book displayed a never-before published photograph of Giorgios Papadopoulos, which the coup later installed as dictator, on a hunting trip with Greek American CIA agents.
On a number of occasions Papahelas has advocated for effective investigative journalism in Greece. The most well-known instance was on May 30, 2010, when he exposed a trail of offshore companies behind former Defense Minister Akis Tsochatzopoulos’ real estate assets. The former Minister later denied the allegations during an interview with Papahelas and Tasos Telloglou.
In 2014 he was presented with the John Dewey Award for Distinguished Public Service from Bard College, awarded annually to alumni of the college fore extraordinary contributions to the public interest. The magazine Politico included Papahelas as one of 27 most influential Europeans in the European Union.
Papahelas was won a number of journalism awards, including journalist of the year, for his personal work and reports of his television programs.
He has contributed columns for the New York Times and the Guardian and has been a guest at meetings of the Bilderberg Club. He is general secretary of the Greek Foundation for European and Foreign Policy (ELIAMEP).