In 1939 his father and two brothers moved to Toronto and founded a roofing company, but his mother remained in Glasgow with the children until after World War II.

During this time he became disillusioned with mathematics, and after sitting in on a linguistics course taught by Eric Hamp, he became more and more interested in the subject and began taking language courses; on his return to America, he applied to the new linguistics graduate program at MIT and was accepted, spending the next three years as a member of the first Ph.D. class there.

He worked as a research assistant with the Mechanical Translation group in 1962 and 1963, and in 1965 he received his doctorate for a dissertation under Noam Chomsky on The accentual system of modern standard Japanese.

At the time of his passing, he was working on two books, a collection of his recent articles and a text on the relation of philosophy of science to linguistics.

Under the pseudonym "Quang Phúc Đông" (supposedly a linguist at the fictitious South Hanoi Institute of Technology), McCawley wrote a paper on "English sentences without overt grammatical subject."