UMavivi Manzini wazalelwa e-Alexandra Township, ngaphandle kweGoli, iTransvaal (manje eyiGauteng) ngo-1956, wabe esethuthela eSoweto. UManzini wahlaselwa yisifo sesifuba esemncane futhi ngenxa yalokho wahlala eduze kweminyaka emine esibhedlela waze waba neminyaka eyi-6. Abazali bakaManzini, ababengothisha, bobabili babengamalunga asebenzayo e-African National Congress (ANC) ngawo-1950. UManzini uqobo waba nesandla kwezepolitiki ngesikhathi esesikoleni esiphakeme, lapho ejoyina iSouth African Student Movement (SASM) ngo-1973. Waqhubeka nezifundo zakhe eTurfloop University eNyakatho Transvaal, lapho wasebenza khona kanzima ukuze azimele kwezepolitiki yize iSouth Africa yayivinjelwe. Inhlangano yabafundi i-African Student Organisation (SASO) kanye nokuxoshwa, ukuvalwa kanye nokufakwa ejele kwezitshudeni eziningi zabafundi eMkhandlwini Omele Abafundi. UManzini wazibandakanya ku-ANC ngomshoshaphansi ngonyaka we-1975. Wasiza uphiko lwezempi lwe-ANC uMkhonto we Sizwe (MK) ngokuphinda futhi ahlinzeke ngolwazi ngendawo nemisebenzi yamaphoyisa endaweni yaseNyakatho Transvaal, ayazi kahle. Lokhu kuhlangana ne-ANC kwanikeza uManzini nezishoshovu ezikanye naye imfundo yezepolitiki, njengoba behlinzekwa ngezincwadi zezombusazwe ezivinjelwe futhi bahlala belalela iRadio Freedom, eyayisakazwa yi-ANC isuka eLusaka, eZambia ukuhlinzeka iNingizimu Afrika imininingwane mayelana naleso sikhathi- ivinjelwe i-ANC.