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- Wanda Gag, artist and children's book author
- André Gide, author
- Allen Ginsberg, Beat poet
- Mary Gladstone, British political diarist
- Joseph Goebbels, Adolf Hitler's Propaganda Minister
- Francine du Plessix Gray, author
- Charles Greville (1794–1865), English civil servant and cricketer
- Eugénie de Guérin
- Che Guevara Revolutionary, kept diaries of his travels and of the wars he fought in
- Alec Guinness, British actor
- Charlotte Forten Grimké, abolitionist and women's rights activist
- Peter Hagendorf, mercenary soldier in the Thirty Years' War
- Richard Hammond, Top Gear Presenter
- Eric Harris and Dylan Klebold, perpetrators of the Columbine High School massacre
- Keith Haring, artist
- Rutherford B. Hayes, 19th president of the United States
- Hedwig Elizabeth Charlotte of Holstein-Gottorp
- Philip Henslowe, Elizabethan theatrical entrepreneur
- Etty Hillesum, young Jewish victim of Nazi Germany
- George Hilton (1673–1725) (diary 1699–1723)
- Edmund C. Hinde (1830-1909), Documented experiences in the California Gold Rush in the 1850s.
- Henry Hitchcock, served under General William Tecumseh Sherman
- Louisa Gurney Hoare (1784–1836), writer on education
- Richard Hoare, second baronet (1758–1838), English antiquary on his travels in Europe and the British Isles
- Lady Margaret Hoby, 1599–1605
- Karen Horney, psychoanalyst
- Gerard Manley Hopkins, poet
- John Hunton, 1839–1928, kept diaries documenting his daily frontier life in Wyoming, knew and wrote about many famous Old West characters
- Julia, Lady Inglis, diarist of the 1857 Siege of Lucknow
- Arthur Crew Inman, author of a 17-million word diary
- Alice James, sister of Henry James and William James: lived in England during the 1880s and 1890s
- Derek Jarman, painter and filmmaker
- Arthur Jessop (1639–1727), West Yorkshire apothecary
- Carolina Maria de Jesus, Brazilian writer, activist
- Liz Jones, writer and journalist
- William Jones, 1755–1821, vicar of Broxbourne (diary 1777–1821)
- Ernst Jünger, writer, Wehrmacht officer
- Franz Kafka, writer
- Frida Kahlo, painter
- Alfred Kazin, literary critic
- Friedrich Kellner, Justice Inspector and author of My Opposition
- Frances Anne Kemble, actress
- Søren Kierkegaard, philosopher
- Francis Kilvert, described rural Victorian life
- Lincoln Edward Kirstein American writer, impresario, and co-founder of the New York City Ballet
- Aya Kitō, chronicled her 10 year battle with spinocerebellar degeneration and author of 1 Litre of Tears
- Käthe Kollwitz, artist, 1867–1945
- John MacDonald, diarist, Memoirs of an eighteenth century footman (1745–1779)
- William Lyon Mackenzie King, Canadian prime minister
- Victor Klemperer, professor of literature, described life as a Jew under the Nazis
- Selma Lagerlöf, first female winner of the Nobel Prize for Literature
- Luca Landucci, Florentine apothecary
- Mark Latham, Australian politician
- James Lees-Milne, biographer and historian, secretary of the Country House Committee of the National Trust 1936–1950
- Madeleine L'Engle, author
- Elisabeth Leseur
- Anne Morrow Lindbergh, wife of the aviator, kept diaries her whole life and describes in detail what the family experienced as a result of the kidnapping of their child
- Courtney Love, actress and rock musician
- Henry Machyn, 16 century London diarist
- Charles Malik, philosopher and diplomat
- Thomas Mann, German novelist and winner of the Nobel Prize for Literature
- Judith Malina, actress, cofounder of the Living Theatre
- John Manningham, lawyer, 1602–1603
- Katherine Mansfield, author
- Florida Scott-Maxwell, actress, analytical psychologist
- Megan McCafferty, YA author
- Matsuo Bashō, haiku and renga poet also known for his travel diaries
- Michinaga, 11th century de facto Japanese ruler
- John Milward (1599–1670) (diary 1666–1668)
- Alanis Morissette, Canadian singer-songwriter
- Helena Morley (1880–1970), described life as a teenage girl in the Brazilian town of Diamantina during the 1890s
- Roger Morrice, Puritan minister and political journalist
- Arthur Munby, Victorian poet, barrister, and solicitor
- Iris Murdoch, author
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