But his progress was so rapid that in two or three years he was able to take his master's place at the lecture-table, and Fourcroy and Vauquelin were so satisfied with his performance that they procured for him a school appointment in 1797 as teacher of chemistry, and in 1798 one as repetiteur at the Ecole Polytechnique.
He was appointed "repetiteur" at the Ecole des Hautes Etudes on its foundation in 1868.
His next post was that of repetiteur at the Ecole Polytechnique, where in 1846 he was appointed professor, and in 1850 he succeeded Gay-Lussac in the chair of chemistry at the Museum d'Histoire Naturelle, of which he was director, in succession to M.
Immediately after finishing his course at the Ecole Polytechnique he was appointed repetiteur there, an office which he had discharged as an amateur while still a pupil in the school; for it had been the custom of his comrades often to resort to his room after an unusually difficult lecture to hear him repeat and explain it.
As a teacher of mathematics Poisson is said to have been more than ordinarily successful, as might have been expected from his early promise as a repetiteur at the Ecole Polytechnique.
He became aspirant repetiteur at the lycee of Rheims in 1853, and after holding several intermediate positions was appointed in 1862 to the professorship of chemistry in Sens lycee, where he prepared the thesis on electromotive force which gained him his doctor's degree at Paris in the following year.