“History is a set of lies agreed upon” has usually been credited to Napoleon Bonaparte (1769-1821)—“La vérité historique est souvent une fable convenue.” However, in 1758, “l’hisloire n’est qu’une fable convenue” was credited to French author Bernard Le Bouyer de Fontenelle (1857-1757). It’s likely that Fontenelle coined the saying, but it’s not known when he first wrote it.
 
The saying was popular in English by the late 1800s. Wendell Phillips (1811-1884), an American abolitionist, said in a speech at Harvard in 1881:
 
“Education is not the chips of arithmetic and grammar,—nouns, verbs, and the multiplication table, neither is it last year’s almanac of dates, or series of lies agreed upon, which we so often mistake for history.”
 
 
Wikipedia: Bernard Le Bouyer de Fontenelle
Bernard Le Bovier de Fontenelle (11 February 1657 – 9 January 1757), also called Bernard Le Bouyer de Fontenelle, was a French author. In 1935, the lunar crater Fontenelle was named after him.
 
Wikipedia: Wendell Phillips
Wendell Phillips (November 29, 1811 – February 2, 1884) was an American abolitionist, advocate for Native Americans, orator and lawyer.
     
Google Books
De L’Esprit
By Claude Adrien Helvétius
Paris: Chez Durand
1758
Pg. 592:
... les historiens ne rapportent que les motifs apparents , ils ignorent les véritables ; ôc c’est , à cet égard, qu’on peut, d’après M. de Fontenelle, assurer que l’hisloire n’est qu’une fable convenue.
 
Google Books
An Enquiry Into the History of Scotland:
Preceding the Reign of Malcolm III or the Year 1056
By John Pinkerton
Edinburgh: James Ballantyne and Co.
1814
Pg. 231:
Indeed this weakness is common to the wisest of us; and thence it is, that owing to our natural love of falsehood, all human history is justly thought, by many thinking men, to contain an infinitely greater number of fables than truths. L’Histoire n’est qu’une fable convenue, says Fontenelle.
 
Google Books
The Scholar in a Republic:
Address at the centennial anniversary of the Phi Beta Kappa of Harvard College
June 30, 1881
By Wendell Phillips
Boston, MA: Lee and Shepard, Publishers
1881
Pg. 13:
Education is not the chips of arithmetic and grammar,—nouns, verbs, and the multiplication table, neither is it last year’s almanac of dates, or series of lies agreed upon, which we so often mistake for history.
 
Google Books
The Blood of Abel
By Wilbur Franklin Bryant
Hastings, NE: The Gazette-Journal Company
1887
Pg. 67:
Yet Napoleon said that history it but a series of lies, agreed upon.
 
Google Books
Abraham Lincoln:
Was He a Christian?
By John Eleazer Remsburg
New York, NY: The Truth Seeker Company
1893
Pg. 82:
“History,” said Napoleon, “is a set of lies agreed upon.”
 
Google Books
The Other Side of the Declaration of Independence:
A Lecture
By Frank Bergen
At Westminster Chapel, Elizabeth, N. J.
December 16th, 1897.
Elizabeth, NJ: Elizabeth Journal Print.
1898
Pg. 7:
We may not agree with the remark of the late Wendell Phillips that history for the most part is a series of lies agreed on; nor refuse to hear history read as Walpole refused, because he said history must be false; but it must be conceded that much of our history of the revolutionary era is fiction written in gush.
 
Google Books
The Heritage and Challenge of History
By Paul Keith Conkin and Roland N. Stromberg
New York, NY: Dodd, Mead
1971
Pg. 78:
There is a gradual growth throughout the century of the skeptical view, already expressed by Napoleon: history is a set of lies agreed upon (une fable convenue).
   
New York (NY) Times
Topics; Making History; Dear Diary
Published: April 26, 1983
What Napoleon said was, ‘‘History is a set of lies agreed upon.’’ What Hitler said was - well, who can be sure? The 60 volumes of his supposed diaries discovered by Stern, the West German magazine, may or may not be lies; they surely are not agreed upon.
 
Google Books
Peter’s Quotations:
Ideas for Our Time
By Laurence J. Peter
New York, NY: Quill/Morrow
1993
Pg. 246:
History is a set of lies agreed upon. — Napoleon Bonaparte (1769-1821)
   
Google Groups: alt.quotations
William C. Waterhouse
8/15/03
(...)
First, the phrase in French is “une fable convenue”; literally, this is “a story agreed-upon.” The past participle “convenu(e)” can mean literally “agreed upon”, as in “l’heure convenue”, the time agreed upon; it can also have a sense of “conventional” and from that occasionally “not heartfelt.” It does not usually suggest outright falsehood.

Second, Napoleon used the phrase but disclaimed originality. In one of his conversations recorded in Las Cases’ _Memorial de Ste Helene_, Napoleon said:

Mais qu’est alors cette ve’rite’ historique, la plupart du temps? Une fable convenue, ainsi qu’on l’a dit fort inge’nieusement.
 
[But what then is this historical truth, most of the time? Une fable convenue, as someone very ingeniously said.]
 
Third, a search through a computer-searchable database finds two authors (Helvetius, _De L’Esprit_, 1758; L.-S. Mercier, _Du Theatre_, 1773) both quoting it and attributing it to Fontenelle (that is, Bernard de Fontenelle, 1657-1757).  I have not yet traced it in Fontenelle, but it seems almost certain to be his.
 
William C. Waterhouse
Penn State