| Mabon | Man | Welsh Names |
| Mabyn | Woman | Welsh Names |
| Macsen | Man | Welsh Names |
| Maddock | Man | Welsh Names |
| Madoc | Man | Welsh Names |
| Madog | Man | Welsh Names |
| Madrona | Woman | Welsh Names |
| Madwen | Woman | Welsh Names |
| Mair | Woman | Welsh Names |
| Mairwen | Woman | Welsh Names |
| Mared | Woman | Welsh Names |
| Marged | Woman | Welsh Names |
| Medi | Woman | Welsh Names |
| Megan | Woman | Welsh Names |
| Meghan | Woman | Welsh Names |
| Meilyr | Man | Welsh Names |
| Melangell | Woman | Welsh Names |
| Menna | Woman | Welsh Names |
| Meredith | Unisex | Welsh Names |
| Mererid | Woman | Welsh Names |