Justice Anastasia Msosa was born in a rural village in 1950 in Malawi. She went to Bunda College of Agriculture and from there applied to law school at Chancellor College after completing the admission requirement of two years of work experience at Chancellor. She earned a Bachelor of Law in 1975.

From there, Msosa worked on behalf of the state in both civil and criminal cases as a government lawyer. Msosa served as a legal advocate, principle legal advocate, and eventually a chief legal advocate in a span of 13 years. She then began to represent those who could not afford a lawyer in the Department of Legal Aid until 1990. She became Register General in 1990 and then became a judge in 1992.

After 1992, she was the first appointed female judge in the High Court. In 1997, she became the first female Justice of the Supreme Court of Appeals. Additionally, Msosa served as the chairperson of the Malawi Electoral Commission (MEC) from 1993 to 1997. During that time period, Malawi became a multiparty democracy. She was re- appointed to the MEC in 2005 and served another 2 terms until 2012. Following her MEC appointment, in a historical moment, Msosa became the first woman Chief Justice of the Supreme Court of Malawi and served in the position from 2013 until 2015.