[4] Johan began to study mathematics at the Royal Academy of Turku (Åbo Kungliga Akademi) when he was fifteen.

[5][6][7] Bergman founded an important research school, and many of his students, including Gadolin, Johan Gottlieb Gahn, and Carl Wilhelm Scheele, became close friends.

[8][9] Gadolin was fluent in Latin, Finnish, Russian, German, English and French in addition to his native Swedish.

He worked with Lorenz Crell, editor of the journal Chemische Annalen in Germany, and with Adair Crawford and Richard Kirwan in Ireland.

Gadolin became the ordinary professor of chemistry at the Royal Academy of Turku in 1797,[11] after the death of Pehr Adrian Gadd.

[4] Gadolin's Inledning till Chemien (1798) was the first chemistry textbook in the Nordic countries that questioned the theory of phlogiston and discussed the role of oxygen in combustion in a modern way.

In 1792 Gadolin received a sample of black, heavy mineral found in a quarry in a Swedish village Ytterby near Stockholm by Carl Axel Arrhenius.

[17] By careful experiments, Gadolin determined that approximately 38% of the sample was a previously unknown "earth", an oxide which was later named yttria.

[22] He described the disproportionation reaction: Having established the composition of Prussian blue, Gadolin suggested a method for precipitating ferrous iron as ferro ferricyanide, preceding the work of Gay-Lussac by forty years.

[23] Reports of many of Gadolin's chemical investigations appeared in German in Crell's Chemische Annalen für die Freunde der Naturlehre, Arzneygelahrheit, Haushaltungskeit und Manufacturen.

In 1825 he published Systema fossilium analysibus chemicis examinatorum secundum partium constitutivarum rationes ordinatorium, a system of mineral classification based upon chemical principles.