In the life of Gay-Lussac the Revolutionary period (or more precisely the period after 1795) was the time when he received his basic scientific education. During the succeeding period of the Consulate Gay-Lussac was a research assistant to Berthollet, while the ten years of the Empire (1804–14) were for him a period of intensive scientific research. By the Restoration of 1815 Gay-Lussac had established an international reputation for himself. A French ‘Who's Who’ published in 1817 described him as ‘one of the most distinguished physicist-chemists of the capital’. He was now a part of the establishment. He came to replace Berthollet all the more naturally as his master had taken the eclipse of Napoleon as a time to withdraw from the public scene. Although Gay-Lussac had benefited indirectly through Berthollet by Napoleonic patronage he had never been formally associated with the imperial regime. Thus he could serve the restored Bourbon monarchy with a clear conscience, although perhaps not without a tinge of regret for old times. It was under the constitutional monarchy of Louis Philippe that Gay-Lussac reached his peak of power and influence.

There may be some scientists whose whole life is in their laboratories. But, if a scientist applies his special expertise in commerce and industry, he obviously relates to the wider world outside the laboratory. If he accepts rewards for such work, he becomes involved in the society of his time. This is all the more so if the rewards are substantial, enabling the scientist to aspire to a superior social position. But science, through its applications, can relate not only to private life but also to public life. If a scientist stands as a member of parliament, he immediately becomes a public figure. If in the course of his public office he expresses opinions on government policy and legislation affecting science and technology, then he is fully involved in contemporary society. Such a man was Gay-Lussac. He did not divide his life into two separate compartments: science and private life. In an alphabetical file of his papers we find not only pure science and industrial tariffs together, but also papers on his tax assessment next to papers on electrical instruments.

Gay-Lussac played an important part in the economic life of France not only by his advice on the analysis of coinage but by his many expert contributions to the system of taxation.

The name of Gay-Lussac is remembered in many ways. His work on the density of alcohol–water mixtures is perpetuated in the ‘degrees Gay-Lussac’, which in France have come to replace the medieval ‘degrees proof’ as a means of describing the strength of alcoholic drinks. The ‘Gay-Lussac tower’ was the name given to a vital part of the manufacture of sulphuric acid in recognition of Gay-Lussac's contribution to this industry. The scientist's name is associated with a type of barometer and a burette. He is also commemorated in the mineral ‘Gay-Lussite’ and in Gaylussacia, the botanical name for the huckleberry. Perhaps Gay-Lussac himself would have derived most satisfaction from being remembered above all as the man who formulated two fundamental laws of nature. If his own scrupulous acknowledgement of unpublished antecedents has meant that his law of the thermal expansion of gases is now more generally known as ‘Charles' law’, at least his discovery of the regularity in the ratio of the volumes of combining volumes of gases is still appropriately known, and learned by every elementary student of chemistry as ‘Gay-Lussac's law’. Yet he is so little known as a man that he is listed in the British Library catalogue – a source of international repute – as Gay-Lussac, Nicholas François, although his Christian names were indisputably Joseph Louis.