Tuhia he haere tonu mo tenei whitianga - I te tau 1937, kua uru atu a Moorehead ki nga Kaitākaro Mercury a Orson Welles, hei tetahi o ana kaiwhakaari matua me Joseph Cotten. (I roto i te putanga ki "The Dick Cavett Show" i te Hui-tanguru 19, 1973, i whakaatu ia, i te tau 1922, i tutaki ia ki a Welles (e 15 tau tana taiohi) i te mea e whitu noa iho ona tau i te Waldorf-Astoria Hotel i New York City.) I mahi ia i roto i tana "The Mercury Theatre on the Air" whakarereketanga reo irirangi, ana he mahi auau i te taha o Welles i roto i te raupapa "The Shadow" hei Margo Lane. I te 1939, ka nekehia e Welles te Whare Tapere Mercury ki Hollywood, i reira ia i tiimata ai te mahi mo RKO Pictures. He maha o ana kaiwhakaari reo irirangi i uru atu ki a ia, ana ko Moorehead tana kiriata tuatahi hei whaea o tana ake ahuatanga, a Charles Foster Kane, i roto i te "Citizen Kane" (1941), e kiia ana e te nuinga o nga kaiwhakaari kiriata ko tetahi o nga kiriata pai rawa atu i hangaia. I whakaatuhia a Moorehead i te kiriata tuarua a Welles, "The Magnificent Ambersons" (1942), ana i whakawhiwhia ki te Tohu Kaitito Kiriata o New York me te whakaingoa mo te Tohu Academy
mo tana mahi. I puta hoki ia i roto i te "Journey Into Fear" (1943), he mahinga kiriata Mercury.