Memoir and biography both tell the story of a life, and publishers treat them as different businesses. The distinction runs through acquisition, editing and how each book reaches readers.
One is written from evidence, the other from memory
A biographer builds an account from documents and testimony, and is judged on accuracy, sourcing and the fairness of the interpretation.
A memoirist works from recollection, and readers accept that memory is partial and shaped by hindsight, provided the account is honest about being one person's version.
The two therefore carry different obligations, and a memoir criticised for incompleteness is being measured against the wrong standard.
They are acquired on different evidence
Biography is bought on the subject. A publisher asks whether enough readers care about this life and whether the author can deliver a definitive account.
Memoir is bought on the writing and the specificity of the experience, since the author is usually not famous enough for the name alone to sell copies.
This is why memoir proposals lean heavily on sample chapters while biography proposals lean on research plans and the author's track record.
It also explains why memoir is a route into publishing for new writers, while biography is generally written by people with an established record.
The editing addresses different problems
Editing a biography concentrates on structure, proportion and whether claims are adequately supported across a long chronology.
Editing a memoir concentrates on shape and selection, because a life contains far more material than a book can hold and the art lies in what is left out.
Memoir editing also involves questions about other people who appear in the story, which raises legal and ethical issues biography handles differently.
Marketing reaches different readers
Biography is sold to readers of history and to people already interested in the subject, and coverage runs through those channels.
Memoir is sold on subject matter and voice, reaching readers who have no prior interest in the author but recognise the experience described.
Book clubs and reader recommendation matter far more to memoir for that reason, since the appeal has to be conveyed by someone who has read it.
Where the two overlap
Autobiographies by well-known figures are sold like biography, on the name, while being written like memoir.
The hybrid frequently disappoints both audiences, because readers expecting a documented record encounter recollection, and readers expecting a voice encounter a career summary.