| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Mervin | MUR-vin (English) | Welsh, English | ||
| Mervyn | MUR-vin (English) | Welsh, English | ||
| Meuric | - | Welsh | ||
| Meurig | - | Welsh | ||
| Mihangel | - | Welsh | ||
| Modred | - | Welsh Mythology, Arthurian Romance | ||
| Mordred | - | Welsh Mythology, Arthurian Romance | ||
| Morgan (1) | MAWR-gən (English) | Welsh, English, French | ||
| Morwen | - | Cornish, Welsh | ||
| Morwenna | - | Cornish, Welsh | ||
| Mostyn | - | Welsh | ||
| Myf | - | Welsh | ||
| Myfanwy | - | Welsh | ||
| Myrddin | - | Welsh Mythology |