In 1975, Mante was employed by the World Bank Group in Washington in the District of Columbia as a project manager.[4][5] In 1983, he was seconded by the World Bank to the International Finance Corporation where after ten years; in 1993, he rose to occupy the management position of Director of the Sub-Saharan Africa Department.[6] In 1997, he was moved to become the Director of the Agribusiness Department of the International Finance Corporation.[7]
During his IFC career, he served on the boards of a number of equity funds and organisations which include the Africa Emerging Markets Fund, West Africa Growth Fund,[8] African Management Services Company, and the Caribbean Financial Services Corporation.[9] He left the World Bank Group in 2000.[3]
In 2001, Mante became a special advisor to the economic management team of the Ghanaian government. He remained a special advisor to the government for the full length of the first-term presidential administration of John Kufuor in Ghana which ended in 2005.[10]
Mante was chairman of the board of Ecobank Ghana from 2006 to 2010.[11][10][12] His time as chairman, saw the introduction of a medium-term goal of shifting Ecobank Ghana from a predominant wholesale bank into a retail bank.[10][13] In 2014, he was elected a non-executive director of the board of Ecobank Transnational as a representative of the bank's West African shareholders. On the board, he was selected as vice-chairman to Emmanuel Ikazoboh who was selected as chairman. Mante retired from the board in 2020.[3][14]
Mante was an independent member of the investment committee of the equity fund, Pan-African Investment Partners from 2002 to 2010. Mante is currently a member of the investment committee of the West Africa Emerging Market Growth Fund.[3]