In 2009, Schmitt was appointed as an ad-hoc judge at the European Court of Human Rights (ECHR).
He is one of two authors of the standard German commentary on criminal procedure,[1] which includes the annotation of the European Convention on Human Rights (ECtHR).
In 2010, he unsuccessfully ran against Angelika Nußberger in the election to succeed Renate Jaeger as the judge representing Germany at the European Court of Human Rights.
[2] In December 2014, Schmitt was proposed as a judge at the International Criminal Court by the German government.
[7] His nine-year term at the ICC ended in March 2024, but he is continuing in office pursuant to Article 36 (10) of the Rome Statute to complete the trial of Alfred Yekatom and Patrice-Edouard Ngaïssona.