The service was held at The Christian Cathedral in Springfield, Massachusetts, on Friday by Archbishop Timothy Paul of the Holy Christian Orthodox Church. The Church is relatively new and despite the name is not part of the Orthodox family of churches.
Speaking in July 2014 after it was announced the American Baptist minister and civil rights campaigner had been nominated for the honour, Archbishop Paul said: "Dr. King was Catholic because he inspired the universal church.
Yesterday Martin Luther King became a saint in the Orthodox Church.#stmlk— Timothy Paul (@TheBasilica) September 10, 2016
"He was evangelical because of his Baptist roots, and he was charismatic. The Roman Catholic Church cannot make him a saint because he was not a Roman Catholic.
"But our church body, which has full apostolic succession, can present him to the entire Christian faith to be venerated on April 4, the date of his assassination."
A leader of the American Civil Rights Movement, Dr King Jr spearheaded non-violent campaigns in the late 1950s and 60s, calling for African-Americans living across the United States to be given legal equality.
Dr King Jr, who became the youngest winner of the Nobel Peace Prize, died at the aged of 39 when he was assassinated at the Lorraine Motel in Memphis, Tennessee, on April 4, 1968.