- THOMAS, JOHN (Siôn Wyn o Eifion; 1786 - 1859), poet
- THOMAS, JOHN (Ieuan Ddu; 1795 - 1871), musician
- THOMAS, JOHN (1757 - 1835) Penfforddwen,, poet
- THOMAS, JOHN (1760 - 1849), Calvinistic Methodist minister
- THOMAS, JOHN (Eos Gwynedd; 1742 - 1818), poet
- THOMAS, JOHN (1763 - 1834), hymn-writer
- THOMAS, JOHN (1838 - 1905), photographer
- THOMAS, JOHN (1857 - 1944), minister (B) and author
- THOMAS, JOHN EVAN (1810 - 1873), sculptor
- THOMAS, JOHN EVAN (1884 - 1941), teacher and writer
- THOMAS, JOHN LUTHER (1881 - 1970), minister (Congl.)
- THOMAS, JOHN ROWLAND (1881 - 1965), religious leader and prominent merchant
- THOMAS, JOHN STRADLING (1925 - 1991), Conservative politician
- THOMAS, JOHN WILLIAM (Arfonwyson; 1805 - 1840), mathematician
- THOMAS, JOSEPH (1814 - 1889), Calvinistic Methodist minister
- THOMAS, JOSEPH MORGAN (1868 - 1955), minister (U) and Free Catholic, councillor and public figure
- THOMAS, JOSEPH WILLIAM (1846 - 1914), chemist
- THOMAS, JOSHUA (1719 - 1797), Baptist minister and historian
- THOMAS, JOSHUA (d. 1759?), cleric and translator
- THOMAS, LAURA EMILY (1822 - 1883), evangelist - see THOMAS, NATHANIEL
- THOMAS, LAWRENCE (1889 - 1960), archdeacon
- THOMAS, LEWIS (d. March 1704), one of the chief leaders of the Particular Baptists
- THOMAS, LEWIS (1568 - 1619), cleric and author
- THOMAS, LEWIS (1832 - 1913) Queensland, pioneer of coal-mining
- THOMAS, LEWIS (fl. first half of the 20th century) south Wales, pioneer of the art of Cerdd Dant
- THOMAS, LEWIS JOHN (1883 - 1970), missionary in India with the London Missionary Society
- THOMAS, LEWIS JOHN WYNFORD VAUGHAN- - see VAUGHAN-THOMAS, LEWIS JOHN WYNFORD
- THOMAS, LOUIE MYFANWY (Jane Ann Jones; 1908 - 1968), novelist
- THOMAS, LUCY (1781 - 1847), pioneer of the Welsh coal industry - see LEWIS, Sir WILLIAM THOMAS
- THOMAS, MANSEL TREHARNE (1909 - 1986), composer, conductor, BBC Wales Head of Music
- THOMAS, MARGARET (1779 - ?), hymnwriter
- THOMAS, MARGARET HAIG (VISCOUNTESS RHONDDA), (1883 - 1958), author, editor and chairperson of companies
- THOMAS, MARGARET HAIG (1883 - 1958), suffragette, editor, author and businesswoman
- THOMAS, MESAC (1816 - 1892), colonial bishop
- THOMAS, MICAH (1778 - 1853), Baptist minister and academy tutor
- THOMAS, MORRIS (1874 - 1959), minister (Calvinistic Methodist), writer and historian
- THOMAS, NATHANIEL (1818 - 1888), Baptist minister
- THOMAS, NATHANIEL (1730), editor
- THOMAS, NICHOLAS (d. 1741), printer and publisher
- THOMAS, Sir NOAH (1720 - 1792), medical man
- THOMAS, OLIVER (1598 - 1653?), Puritan cleric, and author
- THOMAS, OWEN (1812 - 1891), Calvinistic Methodist minister and author
- THOMAS, Sir (1858 - 1923), agriculturist, soldier, and Member of Parliament
- THOMAS, Sir PERCY EDWARD (1883 - 1969), architect and planning consultant
- THOMAS, PERCY GORONWY (1875 - 1954), professor of English
- THOMAS, PHILIP EDWARD (1878 - 1917), poet
- THOMAS, R. S. - see THOMAS, RONALD STUART
- THOMAS, RACHEL (1905 - 1995), actress
- THOMAS, REES URIJAH (1839 - 1901), chairman of the Congregational Union - see THOMAS, DAVID
- THOMAS, RHYS (1720? - 1790), printer