Garrett began his academic career at Columbia University, where he became a full Professor of Psychology at Columbia in 1943. Meanwhile, he served as the Chair of its Psychology Department from 1941 to 1955. In the 1950s Garrett helped organize an international group of scholars dedicated to preventing "race-mixing", preserving segregation, and promoting the principles of early 20th century eugenics and "race hygiene". Garrett was a strong opponent of the 1954 United States Supreme Court's desegregation decision in "Brown v. Board of Education", which he predicted would lead to "total demoralization and then disorganization in that order." He had given testimony favoring secondary school segregation in the Virginia case that was combined into Brown.