American anthropologist noted for his explorations of science and religion in small-scale societies.

Wallis was a Rhodes scholar at the University of Oxford (1907), and his interest in cultural anthropology and his approach to anthropological method were influenced by Sir E.B. Tylor, one of the foremost British anthropologists of the time. Returning to the United States, he continued his education and did ethnographic fieldwork among the Mi'kmaq (Micmac) Indians of eastern Canada (1911–12) and the Canadian Dakota (1914). Primitive religion emerged as one of his chief concerns, and his Messiahs: Christian and Pagan (1918) is a pioneer work in the anthropological study of messianism. He taught at the University of Minnesota from 1923 to 1954.

Wallis' exploration of questions relating to custom, belief, cultural diffusion, and comparative anthropological method perpetuated the tradition of Tylor. Wallis wrote several monographs in collaboration with his wife, Ruth Sawtelle Wallis, among them The Canadian Dakota (1947) and The Malecite Indians of New Brunswick (1957). He also wrote Messiahs: Their Role in Civilization (1943) and (with J.E. Longhurst) Culture Patterns in Christianity (1964).