- Macarius of Alexandria, Hermit
- Magloire, Abbot of Dol in Brittany
- Malachy d’Armagh, Primate of Ireland
- Mammertus, Archbishop of Vienne
- Marcellinus, Bishop of Embrun
- Marcellus I, Pope and martyr
- Marcellus, the Centurion and His Children, Martyrs
- Marcus and Marcellianus, Martyrs
- Margaret of Antioch, Virgin and Martyr
- Margaret of Cortona, Franciscan tertiary, penitent
- Margaret d'Youville, Foundress of the Sisters of Charity, called Grey Nuns
- Margaret Mary Alacoque, Virgin, Apostle of the Sacred Heart
- Margaret Bourgeoys, Foundress
- Margaret, Queen of Scotland
- Mark, Evangelist
- Martha, Virgin
- Martin I, Pope and Martyr
- Martin de Porres, Dominican Coadjutor Brother
- Martin of Tours, Missionary Bishop
- Martina, Martyr
- Martyrs of Japan
- Martyrs of Sebaste
- Martyrs of Uganda
- Mary: Annunciation of the Blessed Virgin Mary
- Mary: the Assumption of the Blessed Virgin Mary
- Mary: the Dedication of Saint Mary of the Snows
- Mary: the Dormition of Mary, Mother of Christ
- Mary: the Immaculate Conception
- Mary: the Immaculate Heart of Mary
- Mary: the Divine Maternity of Mary
- Mary: Miraculous Medal
- Mary: Feast of the Holy Name of Mary
- Mary: the Nativity of the Blessed Virgin
- Mary: Our Lady, Help of Christians
- Mary: Our Lady of Good Counsel
- Mary: Our Lady of Fatima
- Mary: Our Lady of Guadalupe, Patroness of Latin America
- Mary: Our Lady of La Salette
- Mary: Our Lady of Lourdes, (1858)
- Mary: Our Lady of Mount Carmel
- Mary: Our Lady of Perpetual Help, (1863)
- Mary: Our Lady of Ransom or of Mercy
- Mary: Our Lady of the Rosary
- Mary: the Presentation of the Blessed Virgin Mary
- Mary: the Purification of Mary (and the Presentation of Jesus in the Temple) or Candlemas
- Mary: the Seven Sorrows of the Blessed Virgin Mary
- Mary: the Visitation of the Blessed Virgin Mary
- Mary, niece of Abraham, Solitary
- Mary of Egypt, Penitent
- Mary Assunta Pallotta, Franciscan Missionary
- Mary Euphrasia Pelletier, Foundress
- Mary of the Incarnation, Carmelite
- Mary of the Incarnation, Widow, Ursuline nun
- Mary Magdalen, Penitent
- Mary Magdalene of Pazzi, Virgin, Carmelite
- Mary Micaela, Foundress
- Mary of Oignies, Recluse
- Mathilda, Empress
- Matthew, Apostle
- Matthias, Apostle
- Maurice and the Theban Legion, Soldiers and Martyrs
- Maurilius, Bishop of Angers
- Maximilian Kolbe, Martyr
- Maximin or Mesmin of Verdun, Abbot of Micy
- Maximin Giraud, Visionary of La Salette
- Maximus, Bishop of Riez
- Mechtildis of Hackeborn, Abbess
- Medard, Bishop of Noyon and Tournai
- Melanie Calvat, Seeress of La Salette, Virgin
- Meliton, one of the Forty Martyrs of Sebaste
- Mello of Cardiff, Archbishop of Rouen
- Methodius (and Cyril), Apostles to the Slavic Nations
- Michael the Archangel, Protector of the People of God
- Michael the Archangel, Apparition at Monte Gargano, Italy (492)
- Michael Garicoits, Founder
- Michael de los Santos, Trinitarian Priest
- Miraculous Medal
- Modestus, Crescentia (and Guy or Vitus), Martyrs
- Monica, Widow
- Mount Carmel (Our Lady of...)
