* 1802 – Gay-Lussac first published the law that at constant pressure, the volume of any gas increases in proportion to its absolute temperature. Since in his paper announcing the law he cited earlier unpublished work on this subject by Jacques Charles, the law is usually called Charless Law, though some sources use the expression Gay-Lussacs Law.  This law was independently and nearly simultaneously stated by John Dalton.
* 1804 – He and Jean-Baptiste Biot made a hydrogen-balloon ascent; a second ascent the same year by Gay-Lussac alone attained a height of  in an early investigation of the Earth's atmosphere. He wanted to collect air samples at different heights to record differences in temperature and moisture.
* 1805 – Together with his friend and scientific collaborator Alexander von Humboldt, he discovered that the composition of the atmosphere does not change with decreasing pressure (increasing altitude). They also discovered that water is formed by two parts of hydrogen and one part of oxygen (by volume).
* 1808 – He was the co-discoverer of boron.
* 1808 – Discovery and announcement of the law of combining volumes of gases; published in 1809.
* 1810 – In collaboration with Louis Jacques Thénard, he developed a method for quantitative elemental organic combustion analysis by measuring the CO and HO evolved when an organic compound is fully oxidized by potassium chlorate. He also summarised the equation of alcoholic fermentation.
* 1811 – He recognized iodine as a new element, described its properties, and suggested the name iode.
* 1815 – He synthesized cyanogen, determined its empirical formula, and named it.
* 1824 – He developed an improved version of the burette that included a side arm, and coined the terms "pipette" and "burette" in an 1824 paper about the standardization of indigo solutions.