- MEURIG (fl. 1210), poet, and treasurer of Llandaff
- MEURIG ab IDWAL FOEL (d. 986), nobleman of Gwynedd
- MEURIG EBRILL - see DAVIES, MORRIS
- MEURIG GLAN MAWDDACH - see DAVIES, MORGAN
- MEURIG LLWYD Llwyn-y-maen - see LLOYD, EDWARD
- MEURUG ab IORWERTH (fl. c. 1320-1370), one of the last of the 'Gogynfeirdd' bards
- MEURYN - see ROWLANDS, ROBERT JOHN
- MEYLER, JAMES (1761 - 1825), minister (Congl.)
- MEYRICK family Hascard, Fleet, Bush, Wigmore,
- MEYRICK family Bodorgan,
- MEYRICK, EDMUND (1636 - 1712), cleric and benefactor of education
- MEYRICK, Sir SAMUEL RUSH (1783 - 1848), antiquary
- MICHAEL, DAVID (Dewi Afan; 1842 - 1913), poet
- MICHAEL, GLYNDWR ('Major William Martin, RN'; 1909 - 1943), 'the man who never was'
- MICHAEL, JOHN HUGH (1878 - 1959), minister (Meth.), Professor in Methodist colleges in England and Canada, Biblical exegetist
- MICHAELIONES, THOMAS (1880 - 1960), priest and owner of a gold mine
- MIDDLETON, Gwaenynog - see MYDDELTON
- MIDDLETON, DIANA - see BARHAM, DIANA
- MIDLETON, WILLIAM (c. 1550 - c. 1600), poet, soldier, and sailor
- MILBORNE, BLANCHE - see TROY, BLANCHE HERBERT
- MILBOURNE, ANN (d. 1687), landowner - see MORGAN, Sir CHARLES
- MILBOURNE, BLANCHE - see TROY, BLANCHE HERBERT
- MILES, JOHN (1621 - 1683), Particular Baptist leader and American settler
- MILES, WILLIAM JAMES DILLWYN (1916 - 2007), local government officer and author
- MILFORD, 1st Baron - see PHILIPPS, LAURENCE RICHARD
- MILFORD, 2nd Baron - see PHILIPPS, WOGAN
- MILLER, WILLIAM HALLOWES (1801 - 1880), crystallographer
- MILLINGCHAMP, BENJAMIN (1756 - 1829), naval chaplain and collector of Oriental manuscripts
- MILLS, EDWARD (1802 - 1865), popularizer of astronomy
- MILLS, HENRY (1757 - 1820), a pioneer in Welsh congregational singing
- MILLS, JAMES (1790 - 1844), musician - see MILLS, HENRY
- MILLS, JOHN (Ieuan Glan Alarch; 1812 - 1873), Calvinistic Methodist minister, writer and musician
- MILLS, RICHARD (Rhydderch Hael; 1809 - 1844), musician
- MILLS, RICHARD (1840 - 1903), musician - see MILLS, RICHARD
- MILLS, SEBASTIAN BACH (1838 - 1898), pianist
- MILLS-ROBERTS, ROBERT HERBERT (1862 - 1935), surgeon, and association football player
- MINIMUS - see ROBERTS, JOHN
- MITTON, THOMAS - see MYTTON, THOMAS
- MOELONA - see JONES, ELIZABETH MARY
- MOI PLAS - see DAVIES, MORRIS
- MONA - see WILLIAMSON, ROBERT
- MOORE, MARGARET - see LLOYD, MARGARET
- MÔR MEIRION - see MORGAN, RICHARD WILLIAMS
- MORFUDD ERYRI - see FISON, ANNA
- MORGAN family Llantarnam,
- MORGAN family Tredegar Park,
- MORGAN (fl. 1294), rebel
- MORGAN ab IOAN RHUS - see RHYS, MORGAN JOHN
- MORGAN ab OWAIN Lord of Caerleon - see MORGAN ap HYWEL
- MORGAN, JOHN (d. 1504), clerk of parliament, and bishop