Judge Mashangu Monica Leeuw holds a BProc degree from University of the North. In 1987 she obtained her Bachelor of Laws degree at the University of the North West.

In 1978 she was appointed as a prosecutor, until she was appointed as a Regional Court Senior Control Prosecutor in 1978. In 1987 she was appointed as a State Advocate. She was the first black woman to join the Pretoria Bar for the purpose of doing pupillage. She practiced as an Advocate at North West Bar from 1991 to 1997. In 1999 she elevated as a Judge of the High Court. She is one of the first permanent Judges to be appointed in the Labour Appeal Court. She was appointed as the first female Judge President in the Republic of South Africa on the 29th April 2010.

She currently serves on a number of professional and judicial bodies.

Judge Leeuw served as Provincial Secretary: Judiciary in North West Province in 1994, in 1995 she served as an investigator evidence/presenter on the Skweyiya Commission. She was a member of the University of Bophuthatswana Council (Senator representing the Faculty of Law) from 1998 to 1999; from 2001 to 2006 she served as a member of the Board of Trustees of the Lawyers for Human Rights. In 2004 she was the Interim and Permanent member of Council of University of Limpopo up to 2015; she also served as a member of the Committee responsible for the Judicial Training Programme for Aspirant Women Judges in 2006.

She is one of the founder members of the South African Chapter of the International Association of Women Judges. Served as the Regional Representative of the Africa Region and was Provincial Representative in the North West Province of the South African Chapter in 2006 

She is a recipient of the “Onkgopotse Tiro Excellence Award” and also received the first ever Connectional AME Sarah-Allen –Charlotte Maxeke Legacy Award.

Judge Leeuw was appointed by the President to serve as the Chairperson of the Independent Commission for the Remuneration of Public Office Bearers on 15 November 2019.