Rhees taught philosophy at Swansea University from 1940 until 1966, when he took early retirement to devote more time to editing Wittgenstein's works.

[10] Though, as Mario Von Der Ruhr notes, it "marked the beginning, not just of a deep friendship, but of an intense philosophical conversation," Rhees' time as a formal student of Wittgenstein was rather short.

Fergus Kerr identifies remarks in Rhees' nachlass that suggest "fairly sustained Mass-going over a period" and an expressed preference for the Latin mass over 'the vernacular'.

He has been known mainly as a Wittgenstein exegete and for his influence on his friends, colleagues Peter Winch, R. F. Holland, and former student and his literary executor D. Z. Phillips.

For a time, he was visiting professor at King's College London, and with Winch and Norman Malcolm formed a 'formidable triumvirate'[14] of Wittgensteinans.

[15][16] At Swansea Rhees continued to teach, leading weekly post-graduate seminars from 1983 and, in the Cambridge tradition, welcoming a few students in 'at home' sessions for more detailed discussions of their research work.

It was clear in these seminars that Rhees was not only devoted to exegesis of one of the finest thinkers of the twentieth century, but was, in fact, constantly absorbed in developing his own profound insights in philosophy.

He was self-effacing of his capacities and had to be persuaded to accept an honorary professorship at Swansea where he had previously turned down promotion during his teaching career.

Phillips and Peter Winch, containing essays by Cora Diamond, Norman Malcolm, David Cockburn, H. O. Mounce, Raimond Gaita and others.

[7] Numerous posthumous collections of Rhees' published works, notes and manuscripts appeared under the editorship of D. Z. Phillips in the years that followed.