He became a lecturer at the University in 1874, and, after Ludwig Barth von Barthenau became the chair of the department, Weidel could intensify his research on alkaloids.

Although the oxidation of nicotine was already known, Weidel was the first to isolate large enough amounts to determine the properties of the material.

After the retirement of von Barth in 1891, he returned to his previous institute and assumed the position of full professor.

In 1890, Weidel became a member of the Austrian Academy of Sciences and in 1898 he received the Decoration of the Iron Crown of the emperor of Austria.

Without any sign of illness, he delivered his lecture on the morning of June 7, 1899, but died after a few hours from a heart problem.