This children's classic was not written for children butt "to induce kindness, sympathy, and an understanding treatment of horses"—an influence the author attributed to an essay on animals she had read earlier by Horace Bushnell (1802–1876) entitled "Essay on Animals". Her sympathetic portrayal of the plight of working animals led to a vast outpouring of concern for animal welfare and is said to have been instrumental in abolishing the cruel practice of using the checkrein (or "bearing rein", a strap used to keep horses' heads high, fashionable in Victorian England but painful and damaging to a horse's neck). Black Beauty also contains two pages about the use of blinkers on horses, concluding that this use is likely to cause accidents at night due to interference with "the full use of" a horse's ability to "see much better in the dark than men can."
The story is narrated in the first person as an autobiographical memoir told by the titular horse named Black Beauty—beginning with his carefree days as a colt on an English farm with his mother, to his difficult life pulling cabs in London, to his happy retirement in the country. Along the way, he meets with many hardships and recounts many tales of cruelty and kindness. Each short chapter recounts an incident in Black Beauty's life containing a lesson or moral typically related to the kindness, sympathy, and understanding treatment of horses, with Sewell's detailed observations and extensive descriptions of horse behaviour lending the novel a good deal of verisimilitude.