Dassen grew up in Knegsel, studied business administration at Radboud University and worked for ABN AMRO for six years.

[3] Dassen has an older sister and a younger brother, and he attended the Veldhoven secondary school Sondervick College, earning his havo diploma in 2003.

[8][12] Dassen's transition to political life was caused by a variety of factors, including increased nationalism and populism, Brexit and the election of Donald Trump as President of the United States.

[11] Unable to find an established political party that fit him, he joined Volt Europa, who were seeking to form a Dutch wing, in February 2018 and became a volunteer.

[22] Dassen launched a plan with independent politician Pieter Omtzigt in May 2022 to combat corruption among cabinet members and other high-ranking government officials.

[23] A motion to introduce the register was carried, but Minister of the Interior and Kingdom Relations Hanke Bruins Slot refused to execute it.

[24] De Volkskrant reported that some of the other proposals of Omtzigt and Dassen were used by Minister Bruins Slot in her bill for a two-year lobbying ban for former cabinet members.

It contained three plans: to increase the size of the House from 150 to 250 seats, to involve the parliament earlier in bills initiated by the cabinet, and to organize more debates on long-term issues such as the effects of artificial intelligence (AI).

[28] A judge determined that the expulsion had been unjust, and Dassen subsequently apologized to Gündoğan but later stated that the conflict could only be resolved after the withdrawal of her criminal complaint.

[29][30] Her expulsion was finally reinstated in March following a vote by the caucus, in which Dassen supported the move calling their relationship "permanently broken".

Following his studies in Nijmegen, Dassen lived in Rotterdam before moving to Amsterdam, when he became a web and app developer at ABN AMRO.