Hayakawa was educated at the University of Manitoba, McGill University, and the University of Wisconsin. He taught English and language arts at the University of Wisconsin, the Illinois Institute of Technology, the University of Chicago, and San Francisco State College. His first book, Language in Action (1941), was a popular treatment of the semantic theories of Alfred Korzybski and was followed by years of teaching, writing, and lecturing in that field.

In 1968, after a period of student rioting at San Francisco State College, Hayakawa was appointed acting president and immediately took a firm stand against what he regarded as the excesses of student protesters. He acquired a national reputation as a foe of student leftism and a symbol of the conservative in action. In 1969 he was given permanent status as president. He retired in 1973, saying that he had accomplished his mission of restoring order. Three years later he was elected, as a Republican, to the U.S. Senate, where he served for one term.