He attended the School of Theology at the National and Kapodistrian University of Athens, graduating summa cum laude in 1950.

He moved to the United States in 1965, attending the Harvard Graduate School of Arts and Sciences and obtaining his PhD in 1972.

[1] On 18 September 1999, Elder Archbishop Demetrios was enthroned at the Archdiocesan Cathedral of the Holy Trinity as Primate of the Greek Orthodox Archdiocese of America.

[7][8] On 26 November 2015, the Greek Orthodox Archdiocese of America was elevated to the rank of Gerontiki Eparchy (an eparchy headed by a Geron/Elder hierarch) of the Ecumenical Throne, led by Demetrios, with the style of His Eminence Geron Archbishop Demetrios of America.

His brother, Antonios Trakatellis, is a New Democracy MEP for Greece and former Vice-President of the European Parliament.