Rubuta ci gaba ga wannan sakin layi - A shekara ta 1937, Moorehead ya shiga Orson Welles'Mercury Players, a matsayin daya daga cikin manyan masu wasan kwaikwayon tare da Joseph Cotten. (A cikin bayyanar da "The Dick Cavett Show" a ranar 19 ga Fabrairu, 1973, ta bayyana cewa, a cikin 1922, ta haɗu da Welles (shekaru 15 da ƙarami) lokacin da yake ɗan shekara bakwai kawai a Waldorf-Astoria Hotel a Birnin New York.) Ta yi a cikin "The Mercury Theatre on the Air" gyare-gyaren rediyo, kuma tana da rawar gani a gaban Welles a cikin jerin "The Shadow" a matsayin Margo Lane. A shekara ta 1939, Welles ya koma gidan wasan kwaikwayo na Mercury zuwa Hollywood, inda ya fara aiki da RKO Pictures. Da yawa daga cikin masu wasan kwaikwayon rediyo sun shiga tare da shi, kuma Moorehead ya fara fitowa a fim dinsa a matsayin mahaifiyar halayensa, Charles Foster Kane, a cikin "Citizen Kane" (1941), wanda yawancin masu sukar fim suka ɗauka a matsayin ɗayan mafi kyawun fina-finai da aka taɓa yi. An nuna Moorehead a fim na biyu na Welles, "The Magnificent Ambersons" (1942), kuma ya sami lambar yabo ta New York Film Critics Award da kuma lambar yabo ta Academy Award
saboda rawar da ta taka. Ta kuma bayyana a cikin "Journey Into Fear" (1943), wani fim na Mercury.