Roel Mertens has been practicing general civil law for over 35 years. From 1986 to 1995, he served as a research assistant at Maastricht University, and from 1995 to 2023, he worked as an attorney at Paulussen Advocaten.

As of January 1, 2023, he has been serving as a consultant at this firm.
Since 2010, he has also served as a visiting professor of Property Law at the Open University.

He has published numerous articles in various fields of law and several books.