Harris was born and raised in a two-bedroom cottage on the slopes of Bolenowe Carn, a small village near Camborne, Cornwall, in the United Kingdom. At age twelve, he was sent to work at Dolcoath mine where he combined a life of painful labour with the production of poetry celebrating his native landscape around Carn Brea and the scenic splendours of Land's End and the Lizard. He could not afford pen and paper, so instead he improvised and used blackberry juice for ink and grocery bags for paper.
In the 1840s, he married Jane Rule, with whom he had four children: two sons and two daughters. When his second-born daughter, Lucretia, died during Christmas 1855, he produced a moving eulogy. After this a friend found him a more congenial occupation as a Bible-reader or travelling comforter at Falmouth, where he spent the second half of his life. During this period he produced his most important work, the loco-descriptive poem A Story of Carn Brea (1863). He died in 1884 having requested that he should be buried at Treslothan Chapel, near the village of Troon.
There has been some revival of interest in his work, and recently, the book The Cornish Poet was brought out by the John Harris Society, containing his collected works.