MacKenna's prose style was widely admired and he influenced many of his contemporaries, including W. B. Yeats, W. B. Stanford and J. M. Synge.

[6][3][7]In London he collected books, joined the Irish Literary Society and became a member of Young Ireland, a revolutionary group.

[3] Years later, he would write, I have vowed to give one half hour at least every day, at any cost, to reading Irish and modern Greek alternately.

I cannot bear to think of not being able to read Gaelic fluently before I die, and I will not let modern Greek perish off my lips if only by way of homage to the ancient holy land and in the faint hope that someday, somehow, I may see it again with clearer eyes and richer understanding.

By 1905, he expressed an interest in translating the works of the Greek philosopher Plotinus, whose concept of a transcendent “One,” prior to all other realities, he found fascinating.

[10] MacKenna had a high opinion of the capabilities of the language, saying "A man could do anything in Irish, say and express anything, and do it with an exquisite beauty of sound.

[12]MacKenna regretted that he had come to the language too late to use it as a medium of written expression, writing "I consider it the flaw and sin of my life that I didn't twenty years ago give myself body and soul to the Gaelic [i.e. Irish] to become a writer in it..."[11] MacKenna was an ardent Irish nationalist and member of the Gaelic League.

He particularly mourned for his friend and neighbour, Michael O'Rahilly, who was wounded by machine gun fire in Moore Street and left to die over two days.

[15] His investigation of other philosophies and religious traditions drew him back to Plotinus and the intuitive perception of the visible world as an expression of something other than itself, the result of a "divine mind at work (or at play) in the universe.

It seems to me that him alone of authors I understand by inborn sight...[22]Around 1905, while on a trip to St. Petersburg, MacKenna encountered Georg Friedrich Creuzer's Oxford text of Plotinus.

In 1908, MacKenna released an initial rendering of the essay on Beauty (Ennead 1.6) which drew considerable respect from scholars.

[24] By 1912, this initial translation had garnered the attention of English businessman E. R. Debenham who subsequently provided MacKenna with material support for the completion of the work.

[24] With the first version of the First Ennead, MacKenna declared his purpose and method for the translation: The present translation has been executed on the basic ideal of carrying Plotinus' thought—its strength and its weakness alike—to the mind of the reader of English; the first aim has been the utmost attainable clearness in the faithful, full and unalloyed expression of the meaning; the second aim, set a long way after the first, has been the reproduction of the splendid soaring passages with all their warmth and light.

Nothing whatever has been, consciously, added or omitted with such absurd purpose as that of heightening either the force and beauty demand a clarity which sometimes must be, courageously, imposed upon the most negligent, probably, of the great authors of the world.

So do you also: cut away all that is excessive, straighten all that is crooked, bring light to all that is overcast, labour to make all one glow of beauty and never cease chiseling your statue, until there shall shine out on you from it the godlike splendour of virtue, until you shall see the perfect goodness surely established in the stainless shrine.

In 1924, Yeats announced at the Tailteann Games that the Royal Irish Academy had awarded a medal to MacKenna for the translation.

"[32] Sir John Squire similarly praised the translation, writing "I do not think that any living man has written nobler prose than Mr.

"[24] A reviewer in The Journal of Hellenic Studies wrote that "In the matter of accuracy, Mr. MacKenna's translation, which in English at least is pioneer work, is not likely to be final, but for beauty it will never be surpassed.

[3][6][7] James Joyce paid tribute to him in chapter 9 ('Scylla and Charybdis') of his novel Ulysses, with the librarian Richard Best saying, Mallarmé, don't you know, has written those wonderful prose poems Stephen MacKenna used to read to me in Paris.