Asser was professor of commercial and private international law at the University of Amsterdam from 1862 to 1893. In 1869 Asser, along with two associates, started the Revue de Droit International et de Législation Comparée (“Review of International Law and of Comparative Legislation”). He was also a founder of the Institute of International Law in 1873.

In 1891 Asser prevailed upon the Dutch government to convoke the Hague Conference for the Unification of International Private Law, which first met in 1893 and later became a permanent institution, responsible, among other things, for the Hague treaties of 1902–05 concerning family law. In 1911–12 he presided over conferences for the unification of the law relating to international bills of exchange. In 1893 he became a member of the Dutch Council of State. Asser was a Netherlands delegate to the Hague peace conferences of 1899 and 1907.