[5] In 2008, his final year at the University of Zimbabwe, Thabani won both the ICRC national moot court competition with a team that included Fadzayi Mahere and Farai Mushoriwa.
The team went on to win ICRC African moot court competition, where he was named the best speaker in the finals which came with an internship with the United Nations International Criminal Tribunal for Rwanda (ICTR) based in Arusha, Tanzania.
Thabani Mpofu briefly worked as a Legal Researcher in the Office of the Trial Prosecutor and took part in the prosecution of Ephrem Setako.
In 2012, Mpofu represented and won former Prime Minister Morgan Tsvangirai's bid to sue former president Robert Mugabe without seeking the leave of court, becoming the first case of that kind.
In May 2021, Thabani obtained a judgment from three judges of the High Court which held that the term of office of Chief Justice Luke Malaba had come to an end and that the constitutional amendment that had been pushed by the ruling ZANU-PF party did not benefit him.