Whakaotihia te rerenga e whai ake nei: I whānau a Gardiner i te tau 1914 ki Kumasi, Gold Coast, ki roto i te whānau o ngā kaihokohoko angitu. Whai muri i tana haerenga ki Adisadel College, i whakaakona ia i Sierra Leone me te United Kingdom. Whai muri i te otinga o ana akoranga, ka noho a Gardiner hei kaiwhakaako o te ohanga i te Whare Waananga o Fourah Bay. Mai i te 1946 tae noa ki te 1948 i mahi ia hei tohunga mo te UN Trusteeship Council. I te tau 1949 i utua ia hei Kaiwhakahaere Tuatahi mo nga Akoranga Extramural i te Whare Wananga o te Whare Wananga i Ibadan, Nigeria. E wha tau i muri mai ka hoki ia ki te Gold Coast ki te mahi i nga taumata teitei ake o te mahi a te iwi. Whai muri i te rangatiratanga o te whenua hei Ghana i te 1957, i tohua a Gardiner e te Pirimia a Kwame Nkrumah hei Hekeretari Whakahaere. He hononga mahi ngoikore a te tokorua na te mea ko te whakaaro nui o Nkrumah e pa ana ki te momo whakahaere a Gardiner. Whai muri i tana wehenga i te tau 1959, i whakaae a Gardiner ki tana whakaingoatanga hei Tumuaki Tuarua mo te Hekeretari o te UN Economic Commission for Africa (UNECA). I te tau 1960
I pakaru te pakanga a-iwi i te Republic of Congo motuhake hou a Gardiner i uru kaha ki nga mahi a te UN ki te whakatau i te ahuatanga, hei takawaenga i waenga i nga roopu rereke me te kaitohutohu tata ki te Hekeretari-Tianara o te UN U Thant mo tenei kaupapa.