Henri Cassiers was born in Antwerp, Belgium on 11 August 1858. He was a Flemish artist, best known for his applied art: illustrations, posters, wall charts and postcards, often with a maritime theme.

Cassiers trained as an architect and followed his artistic training at the academies of Brussels and Sint-Joost-ten-Node. He quickly developed his own style and focus, focusing on maritime scenes and city and village views, both in Flanders (including Genk) and in the Netherlands. He was particularly attracted by the Dutch costumes, especially those from Zeeland and Katwijk.

He illustrated many popular weekly magazines from 1886 to 1893, such as De Vlaamsche Patriot, Le Globe Illustré and L'Illustration Européenne. In addition, illustrations of him appeared in various books, including those by Camille Mauclair, Emile Verhaeren, Cyriel Buysse and Jean d'Ardenne. In de Guide descriptif illustré de la côte de Flandre (Brussels, 1888) of the latter are no less than 106 drawings by Cassiers.

Cassiers' compositions were as also easily adafted for use for advertising and publicity purposes, especially tourist places and shipping companies regularly commissioned him. The best known was his work for the 'Red Star Line'. From 1898 he made many posters, postcards, menu cards and other advertising materials for this regular service. He was also a member of the Belgian artists' association Les Hydrophiles. In 1994 a large retrospective of his work was shown at the Museum Vleeshuis in Antwerp and the Katwijks Museum in Katwijk, for which a catalog was published.

Henri Cassiers died in Ixelles, Belgium on February 27, 1944.