Susannah Cowen has been practising as an advocate since 2001. She started practising in Cape Town and, in 2010, moved to Johannesburg. She took silk in July 2018.
Her preferred areas of practice are commercial law, constitutional law, administrative law, land law and customary law. She has appeared in the Constitutional Court, the Supreme Court of Appeal, the High Court (various divisions), the Land Claims Court and regulatory tribunals. She has acted as a Judge in the High Court in Johannesburg.

Susannah holds BA and LLB degrees from the University of Cape Town and a BCL degree from the University of Oxford. In 2000 she clerked at the Constitutional Court for then President of that Court, Justice Arthur Chaskalson.