- THOMAS ab IEUAN - see JAMES, THOMAS EVAN
- THOMAS ab IFAN - see EVANS, THOMAS
- THOMAS ap IEUAN - see JAMES, THOMAS EVAN
- THOMAS ap RHODRI (c. 1295 - 1363), nobleman
- THOMAS BRWYNLLYS (fl. c. 1580-1590), poet
- THOMAS DERLLYS (fl. 15th century), poet
- THOMAS GRYTHOR (fl. 17th century), poet
- THOMAS GWYNEDD (fl. 16th century), poet
- THOMAS PENLLYN (d. 1623), poet
- THOMAS TEIFI (fl. 16th century), poet
- THOMAS WALLENSIS (d. 1255), bishop of S. Davids - see WALLENSIS
- THOMAS WALLENSIS (d. 1350), Black Friar - see WALLENSIS
- THOMAS, ALBAN (d. 1740?), cleric, poet, and translator
- THOMAS, ALBAN (1686 - 1771), physician - see THOMAS, ALBAN
- THOMAS, ALFRED (1840 - 1927) Bronwydd,, baron Pontypridd
- THOMAS, ANN (1704 - 1727) - see MADDOCKS, ANN
- THOMAS, ANNA (1839 - 1920) - see FISON, ANNA
- THOMAS, ARTHUR SIMON (Anellydd; 1865 - 1935), cleric and writer
- THOMAS, BENJAMIN (Myfyr Emlyn; 1836 - 1893), Baptist minister, poet, lecturer, and author
- THOMAS, BENJAMIN (1723 - 1790), Independent preacher and Methodist exhorter
- THOMAS, BENJAMIN BOWEN (1899 - 1977), adult educator and civil servant
- THOMAS, CLARA (1841 - 1914), landowner and philanthropist
- THOMAS, CLEMENT PRICE - see PRICE THOMAS, CLEMENT
- THOMAS, DAFYDD (1782 - 1863), hymnist - see THOMAS, ROBERT
- THOMAS, Sir DANIEL (LLEUFER) (1863 - 1940), stipendiary magistrate
- THOMAS, DAVID (d. 1735), poet
- THOMAS, DAVID (Dafydd Ddu Eryri; 1759 - 1822), man of letters and poet
- THOMAS, DAVID (1813 - 1894), Congregational minister and Biblical commentator
- THOMAS, DAVID (1794 - 1882), pioneer of the iron industry in U.S.A.
- THOMAS, DAVID (Dewi Hefin; 1828 - 1909), poet
- THOMAS, DAVID (1739? - 1788), bone-setter
- THOMAS, DAVID (1880 - 1967), educationalist, author and pioneer of the Labour Party in north Wales
- THOMAS, DAVID (1811 - 1875), Congregational minister - see THOMAS, DAVID ALFRED
- THOMAS, DAVID (d. 1780?), minister (Congl.)
- THOMAS, DAVID ALFRED (first viscount RHONDDA), (1856 - 1918), businessman and politician, Liberal Member of Parliament
- THOMAS, DAVID EMLYN (1892 - 1954), politician and trade unionist
- THOMAS, DAVID FFRANGCON (1910 - 1963), cellist
- THOMAS, DAVID JOHN (Afan; 1881 - 1928), musician
- THOMAS, DAVID RICHARD (1833 - 1916), cleric and historian
- THOMAS, DAVID VAUGHAN (1873 - 1934), musician
- THOMAS, DAVID WALTER (1829 - 1905), cleric
- THOMAS, DEWI-PRYS (1916 - 1985), architect
- THOMAS, DYLAN MARLAIS (1914 - 1953), poet and prose writer
- THOMAS, DYLAN MARLAIS (1914 - 1953)
- THOMAS, EBENEZER (Eben Fardd; 1802 - 1863), schoolmaster and poet
- THOMAS, EDDIE - see THOMAS, EDWARD
- THOMAS, EDWARD (Idriswyn; 1847 - 1906), journalist
- THOMAS, EDWARD (Cochfarf; 1853 - 1912), carpenter, politician and Mayor of Cardiff
- THOMAS, EDWARD - see THOMAS, PHILIP EDWARD
- THOMAS, EDWARD WILLIAM (1814 - 1892), musician