[6][7] His Ph.D. thesis at Harvard University was published in 1963 with the title "Grammatical analysis as a part of understanding a sentence".

He worked initially as a Linguistics Researcher and focussed around a language called FASE (Fundamentally Analyzable Simplified English) with the goal of improving communication between humans and computers.

[1] A project which attempted to clarify the authorship of The Federalist Papers connected him to Robert Morris and began his involvement with early Unix development.

[9] McMahon is best known for his contributions to early versions of the Unix operating system, in particular the sed stream editor.

[11] McMahon worked on the creation of a pairing system for go together with Bob Ryder of Bell Labs in the early 1960s.