Little is known of the early life of Father Joachim Alexopoulos. In 1906, Father Joachim Alexopoulos was named the [[priest]] of the [[parish]] of Saint Sophia (Holy Wisdom) in Washington, D.C. He came to the parish after it had been served by Fr. Nathaniel Sederis and itinerant priests for the first two years after it initial organization. Fr. Joachim served at St. Sophia Church until 1918.
In 1920, Fr. Joachim Alexopoulos succeeded Fr. Joachim Malahias as the priest at the Church of the Annunciation in Boston, Massachusetts. <ref>http://www.thecrimson.com/article/1922/10/27/outlines-dangers-of-present-turkish-adjustment/ News article by Reverend Joachim Alexopoulos</ref> Fr. Joachim Alexopoulos came to Annunciation Church at a time when the Greek disasters in Turkey following World War I had caused plans for a new church in Boston to have become dormant. Fr. Joachim revitalized these plans, and a new church was completed in 1924.
On [[June 28]], 1923, Fr. Joachim was appointed the first Greek Orthodox Bishop of Boston with the new Annunciation church, designated a [[cathedral]], as his seat. During the years as the leader of the Greek Orthodox community in the Boston area, Bp. Joachim helped establish and support new parishes among the Greek immigration.