Markwin mainly deals with matters relating to maritime law, liability law and contract law. Markwin's practice is part litigation and part advisory. Amongst his clients are international ship owners and their P&I Clubs, hull underwriters and FD&D Clubs, but also classification societies, charterers and traders in liquid bulk and their underwriters.
From 1995 until 2000 Markwin worked as a staff member for economic and tax affairs at the "Koninklijke Vereniging van Nederlandse Reders" (Royal Association of Netherlands Shipowners).
In 2000 Markwin joined Van Harmelen Beijneveld Van Houten and was sworn in as a lawyer. In 2007 Markwin became a partner of the firm.
Markwin is a former Dutch rowing champion in the lightweight 4- and the 8+. In his spare time, he still enjoys rowing regularly.