The interval of a tritone between C and F♯ is a recurring motif, the occurrence of which unifies the entire work. The interval is used both in contexts that emphasise the harmonic distance between C and F♯ and those that resolve them harmonically, mirroring the theme of conflict and reconciliation present throughout the work. The Requiem aeternam, Dies irae, and Libera me movements end in a brief choral phrase, consisting mainly of slow half notes, that resolves the tritone's discord to an F major chord, while at the end of the Agnus Dei the tenor (in his only transition from the Owen poems to the Requiem liturgy, on the key words, Dona nobis pacem - Give us peace) outlines a perfect fifth from C to G before moving down to F♯ to resolve the chorus's final chord. At the end of the Dies irae, the tenor sings (from Owen's "Futility") "O what, what made fatuous sunbeams toil, to break earth's sleep at all?" The notes of "at all" form the tritone and lead into the choir's formal resolution. In the final Owen setting, "Strange Meeting", one of the most prominent expressions of the tritone is sung by the Tenor, addressing an opposing soldier with the words "Strange friend". This poem is accompanied by sporadic detached chords from two violins and a viola, which include the tritone as part of a dominant 7th chord. At the end of the poem, the final string chord resolves to the tonic, bringing the work to its final, reconciliatory In paradisum. On a more practical level, Britten facilitated musical execution of the tritone in the closing bars by having the F# sung in one voice, but the C in another.

Four other motifs that usually occur together are distinct brass fanfares of the Dies Irae: a rising arpeggio, a falling arpeggio followed by a repeated note, a repeated fourth in a dotted rhythm ending in a diminished arpeggio, and a descending scale. These motifs form a substantial part of the melodic material of the piece: the setting of "Bugles sang" is composed almost entirely of variations of them.

Although there are a few occasions in which members of one orchestra join the other, the full forces do not join together until the latter part of the last movement, when the tenor and baritone sing the final line of Owen's poem "Strange Meeting" ("Let us sleep now…") as "In Paradisum deducant" ("Into Paradise lead them...") is sung first by the boys' choir, then by the full choir (in 8-part canon), and finally by the soprano. The boys' choir echoes the Requiem aeternam from the beginning of the work, and the full choir ends on the resolved tritone motif mentioned above.

For the opening performance, it was intended that the soloists should be Galina Vishnevskaya (a Russian), Peter Pears (an Englishman) and Dietrich Fischer-Dieskau (a German), to demonstrate a spirit of unity. Close to the premiere, the USSR did not permit Vishnevskaya to travel to Coventry for the event. With only ten days notice, Heather Harper stepped in and learned the soprano role.

The premiere took place on May 30, 1962, in the rebuilt cathedral with the City of Birmingham Orchestra, conducted by Meredith Davies (accompanying soprano and chorus), and the Melos Ensemble, conducted by the composer (accompanying tenor and baritone). There was a profound silence between the final notes and the applause. It was a triumph, achieving an impact matched by few works in the twentieth century and accordingly hailed by critics and audiences, at this and subsequent performances in London and abroad, as a contemporary masterpiece. Writing to his sister after the premiere, Britten said of his music, "I hope it'll make people think a bit." On the title page of the score he quoted Wilfred Owen:

"My subject is War, and the pity of War.The Poetry is in the pity…All a poet can do today is warn."

Both the southern hemisphere and the North American first performances took place on the same day, 27 July 1963. The southern hemisphere premiere was in Wellington, New Zealand, with John Hopkins conducting the New Zealand National Orchestra (now the New Zealand Symphony Orchestra) and the Royal Christchurch Musical Society, with soloists Peter Baillie, Graeme Gorton and Angela Shaw. The North American premiere was at Tanglewood, with Erich Leinsdorf conducting the Boston Symphony Orchestra with soloists Phyllis Curtin, Nicholas Di Virgilio, Tom Krause and choruses from Chorus Pro Musica and the Columbus Boychoir.

The Dutch premiere took place during the Holland Festival, in 1964. The Amsterdam Concertgebouw Orchestra and the Netherlands Radio Choir were conducted by Bernard Haitink; the chamber orchestra (consisting of Concertgebouw Orchestra instrumentalists) by Britten himself. The soloists were Vishnevskaya, Fischer-Dieskau and Pears, in their first public performance together.

An interpretation of the work was performed by the English Chamber Choir at Your Country Needs You, an evening of "voices in opposition to war" organised by The Crass Collective in November 2002.