[1] In 2003 he was a visiting professor at the Institut de Droit Canonique of the Université Marc Bloch in Strasbourg, France.
[2] Starting with the 2005–2006 academic year, Martens has been a member of the faculty of the School of Canon Law at The Catholic University of America in Washington, D.C.
[3] He was appointed a counselor to the Committee on Canonical Affairs and Church Governance of the United States Conference of Catholic Bishops in 2008.
Martens has served as editor-in-chief of the scientific journal The Jurist: Studies in Church Law and Ministry since 2012.
He was also the co-founder and co-editor-in-chief of the journal Recht, Religie en Samenleving (Law, Religion and Society).