Justice Agyemang was called to the Ghanaian Bar in 1987 and joined the Bench shortly after. As a Ghanaian judge, she served in various judicial capacities and sat in a number of jurisdictions including Accra, Cape Coast, Koforidua, Kumasi, and Tema. She also served as vice-president of the Association of Magistrates and Judges of Ghana from 1996 to 2000. She was elevated to the High Court in 2002. She began working for the Commonwealth Secretariat as an expert judge in 2004, first being sent to The Gambia where she spent four years as a High Court judge. During her four-year tenure in the Gambia, Justice Agyemang served the Land, Civil, Commercial and Criminal divisions. In 2008, she was seconded to Swaziland where she served for two years in a similar capacity. Her cases in Swaziland spanned both private and public law and included cases on defamation, unlawful arrests, police brutality and electoral disputes. One of her notable judgments in Swaziland was her judgment on the right to free education.
Justice Agyemang returned to The Gambia in 2010, still with the Commonwealth Secretariat, as an expert Appeal Court Judge. She was appointed Chief Justice of the Gambia in August 2013. Her appointment was widely seen as an inspired choice as she is seen by the international community as an experienced and independent minded judge. She served until her abrupt removal in February 2014 with no official reason given for the action. She currently serves as a Justice of the Ghana Court of Appeal. In October 2015, while speaking at the opening ceremony of a new judicial complex in Accra, Ghanaian President John Dramani Mahama cited Justice Agyemang as an example of highly respected judges within the Ghanaian judiciary.