Hans Londonck Sluijk graduated in 1992 with degrees in Law and Political and Social Cultural Studies, beginning his legal career at leading Dutch law firm Houthoff that same year.

Martine Kos initially pursued a career in music, studying as a vocalist at the Royal Conservatory in The Hague. Despite her passion for music, she decided to follow a legal career path, earning her Master's in Dutch Law in 2001. Martine began her legal career at Houthoff in Amsterdam, where she first collaborated with Hans.

By 2002, Hans had already established himself as an insurance and litigation specialist. Martine quickly gained recognition in these fields as well. Their professional collaboration at Houthoff spanned over a decade. In 2015, Martine joined a midsize firm in Utrecht. Despite this move, she and Hans continued to stay in touch and occasionally collaborated on cases for their respective clients. Eventually, Martine and Hans decided to establish their own boutique firm, opening the doors of Londonck & Kos on January 1, 2023.