Musi obtained a Dip Juris, BA and an LLB from UWC and later, a BA Honours and LLM from the University of Cape Town. He worked as a prosecutor from 1986 until 1992, when he was appointed to the magistracy. He was appointed a judge of the Free State High Court in 2005 and has served at a judge of the Labour Court and acted at the Labour Appeal Court. Musi is the chairperson of the Independent Commission for Remuneration of Public Office Bearers.
Musi has previously acted at the Constitutional Court 2016
Key judgments: (1) MARITZ V MUNICIPAL MANAGER: MATJHABENG LOCAL MUNICIPALITY (2050/2016)  ZAFSHC 125 (20 JULY 2017) ;
(2) PT OPERATIONAL SERVICES (PTY) LTD V RETAIL & ALLIED WORKERS UNION ON BEHALF OF NGWELETSANA (2013) 34 ILJ 1138 (LAC) ;
(3) NATAL WITNESS V GOZUNDER & OTHERS (2010) 31 ILJ 2339 (LAC)