M
- Macedonius I of Constantinople
- Mainline Protestant
- Major prophet
- Malankara Orthodox Syrian Church
- Malchus
- Manahen
- Marcionism
- Marcus I of Byzantium
- Mariavite Church
- Mark the Evangelist
- Martha
- Martin Luther
- Martyr
- Martyrs' Synod
- Mary Magdalene
- Mary of Bethany
- Mary of Clopas
- Mary of Rome
- Mary, mother of James
- Mary, mother of Jesus
- Mary, mother of John Mark
- Masoretic Text
- Matthew the Apostle
- Matthew the Evangelist
- Menno Simons
- Mennonite
- Mennonite Church Canada
- Mennonite Church USA
- Mennonite World Conference
- Meqabyan
- Messiah
- Messianic Jewish Alliance of America
- Methodios I of Constantinople
- Methodism
- Methodist Church in Ireland
- Methodist Church of Great Britain
- Metrophanes of Byzantium
- Michael (archangel)
- Michael I Cerularius
- Middle Ages
- Middle East Council of Churches
- Millerism
- Minister (Christianity)
- Ministry of Jesus
- Minor prophet
- Miracles of Jesus
- Missionary
- Modernism in the Catholic Church
- Monk
- Monotheism
- Montanism
- Moravian Church
- Mormonism and Christianity
- Muratorian fragment
- Myrrhbearers