The law was named after scientist Jacques Charles, who formulated the original law in his unpublished work from the 1780s.
In two of a series of four essays presented between 2 and 30 October 1801, John Dalton demonstrated by experiment that all the gases and vapours that he studied expanded by the same amount between two fixed points of temperature.  The French natural philosopher Joseph Louis Gay-Lussac confirmed the discovery in a presentation to the French National Institute on 31 Jan 1802, although he credited the discovery to unpublished work from the 1780s by Jacques Charles. The basic principles had already been described by Guillaume Amontons and Francis Hauksbee  a century earlier.
Dalton was the first to demonstrate that the law applied generally to all gases, and to the vapours of volatile liquids if the temperature was well above the boiling point. Gay-Lussac concurred. With measurements only at the two thermometric fixed points of water (0°C and 100°C), Gay-Lussac was unable to show that the equation relating volume to temperature was a linear function.   On mathematical grounds alone,  Gay-Lussacs paper  does not permit the assignment of any law stating the linear relation.   Both Daltons and Gay-Lussac's main conclusions can be expressed mathematically as:
where  is the volume occupied by a given sample of gas at 100 °C;  is the volume occupied by the same sample of gas at 0 °C; and  is a constant which is the same for all gases at constant pressure. This equation does not contain the temperature and so is not what became known as Charles Law. Gay-Lussacs value for  (), was identical to Dalton's earlier value for vapours and remarkably close to the present-day value of . Gay-Lussac gave credit for this equation to unpublished statements by his fellow Republican citizen J. Charles in 1787.  In the absence of a firm record, the gas law relating volume to temperature cannot be attributed to Charles.
Dalton's measurements had much more scope regarding temperature than Gay-Lussac, not only measuring the volume at the fixed points of water but also at two intermediate points.  Unaware of the inaccuracies of mercury thermometers at the time, which were divided into equal portions between the fixed points, Dalton, after concluding in Essay II that in the case of vapours, “any elastic fluid expands nearly in a uniform manner into 1370 or 1380 parts by 180 degrees (Fahrenheit) of heat”, was unable to confirm it for gases.