

| Macedonia | Clement of Ohrid |
| Madagascar | Vincent de Paul |
| Madrid & Alcala | Justus and Pastor, Isidore the Farmer |
| Magistrates | Ferdinand III of Castile |
| Maids | Zita |
| Maine, USA | Our Lady fo Peace |
| Majorca city | Alonso Rodriguez |
| Majorca island | Alonso Rodriguez |
| Malta | Paul, Apostle |
| Mantua, Italy | Anselm of Lucca, the Younger |
| Marble workers | Clement I, Four crowned martyrs, Louis |
| Marching Auxiliaries | Vitus |
| Mariners | Nicholas of Tolentino |
| Marines (Italian) | Barbara |
| Maritime pilots | Nicholas of Myra |
| Maronites, Maronite Christians | Maro |
| Marriage | John Francis Regis |
| Marriages (unhappy) | Gengulf |
| Married women | Monica |
| Maryland, USA | Our Lady of the Assumption |
| Masons | Thomas, Apostle, Four crowned martyrs, Louis |
| Massachusetts, USA | Our Lady of the Incarnation |
| Medal collectors | Eligius (Eloi) |
| Medical profession | Cosmas and Damian, Luke, Pantaleon |
| Medical technicians | Albert the Great |
| Mentally ill | Dymphna |
| Merchants | Francis of Assisi, Nicholas of Myra, Homobonus |
| Merchants, Italian | Francis of Assisi |
| Merthyr Tydfil, Wales | Tydfil |
| Messengers | Gabriel the Archangel |
| Metalworkers | Eligius (Eloi) |
| Metz, France | Patiens of Metz |
| Mexican young people | John Bosco |
| Mexico | Our Lady of Guadalupe, Joseph |
| Mexico City, Mexico | Philip of Jesus |
| Michigan, USA | Our Lady, Gate of Heaven |
| Midwives | Raymond Nonnatus |
| Migrants | Frances Xavier Cabrini |
| Milan | Ambrose of Milan |
| Millers | Honoratus |
| Milliners (Hatmakers) | James the Greater |
| Miners | Anne (Mother of Mary), Barbara |
| Minnesota, USA | Our Lady, Mother of the Church |
| Miscarriage prevention | Catherine of Sweden |
| Missionary priests | Vincent Pallotti |
| Missioners in Catholic Lands | Leonard of Port Maurice |
| Missioners of the Precious Blood | Francis Xavier |
| Missions | Francis Xavier, Peter Claver, Therese of Lisieux, Leonard of Port Maurice |
| Missions, Polish | Maria Teresa Ledochowska (Bd) |
| Missions, Portuguese | John de Britto |
| Mississippi, USA | Our Lady of Sorrows |
| Missouri, USA | Our Lady of Calvary |
| Mixed race, people of | Martin de Porres |
| Monaco | Devota |
| Monarchy, French | Louis |
| Mongolia, Inner | Immaculate Conception of Mary |
| Mongolia, Outer | Francis Xavier |
| Mons, Belgium | Waltrude |
| Montana, USA | Our Lady of the Pines |
| Monte Marano | John of Monte Marano |
| Montefalco, Italy | Clare of Montefalco |
| Montesanto, Italy | Gerard of Lunel/td> |
| Moral theologians | Alphonsus de Liguori |
| Moravia | Wenceslaus, Cyril and Methodius |
| Moscow | Boris |
| Mothers | Monica, Gerard Majella, Nicholas of Tolentino |
| Motorcyclists | Mary, The Madonna of Castaliazzo or Our Lady of Grace and of Crete |
| Motorists | Frances of Rome, Christopher |
| Motorways | John the Baptist |
| Mountaineers, mountain climbers | Bernard of Montjoux (or Menthon) |
| Mullion, Cornwall | Melaine of Rennes |
| Munich, Germany | Benno |
| Music, musicians | Cecilia, Gregory the Great, Dunstan |
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