He joined the Piarist order and took vows in 1779 and was ordained a priest in 1785 after which he taught at schools in Raseiniai, Vilnius and Szczuczyn.
At Vilnius he also continued his own studies in chemistry and botany with Georg Forster and Jean-Emmanuel Gilibert, and helped create a botanical garden at the university.
After that, saddened by the slow destruction of his beloved botanical garden, his health worsened and he eventually went totally blind.
Despite his religious training Jundziłł adopted naturalism[2] and was one of the first to teach veterinary medicine in Lithuania and was the author of several basic textbooks on botany and zoology.
He was also the author of the first scientifically precise description of the flora and fauna of Lithuania, based on the system of Carl Linnaeus, and won a gold medal for his work Botanika stosowana (Applied Botany).