After graduating as a civil engineer specialising in electronics, she became an assistant at the Catholic University of Leuven in 1982. She prepared her PhD under Professor R. De Keersmaecker of ESAT and Professor W. van der Weg of the University of Utrecht. She obtained her doctorate in September 1987.

After collaborating with Dr Alice White at Bell Labs (USA), she became a senior lecturer at KU Leuven in 1998, a professor in 2001 and a full professor in 2003. She taught courses including Materials Physics for Nanoelectronics and was co-lecturer for the course Semiconductor Physics. She was also the founder and coordinator of the Erasmus Mundus programme for Nanoscience and Nanotechnology.

In 2005, she became Vice-Rector for the Science & Technology Group. She was the second woman to become Vice-Rector at KU Leuven, after Emma Vorlat.^[3] She also became responsible for the Core Facilities for research and responsible for Science & Technology at Kulak.

Maex ran for rector of KU Leuven in 2013. On 13 May, she received 540 votes in the first round, against 567 for Rik Torfs. The other candidates received: Bart De Moor 197 votes and Tine Baelmans 191 votes. In the second round of voting on Friday 17 May 2013, she received 736 votes against 772 for Rik Torfs. Following this result, she decided to leave KU Leuven for the universities of Amsterdam.

From October 2013 to 2016, she was Dean of the Faculty of Science, Mathematics and Informatics (FNWI) at the University of Amsterdam, and of the Faculties of Science (FEW) and Earth and Life Sciences (FALW) at VU University Amsterdam.^[4]

On 1 June 2016, she became rector magnificus of the University of Amsterdam and a member of the Executive Board. She succeeded Dymph van den Boom, who had held this position since 2007. Maex left the UvA on 15 July 2022 to return to her hometown of Leuven.