Like much twentieth-century drama, Murder in the Cathedral was experimental in form. Eliot moved away from nineteenth-century prose drama by writing the play, with the exception of the Christmas sermon and the knights' apologies, entirely in verse.
Eliot felt that verse was a loftier form that better conveyed universal truths when compared to prose, which could sometimes reflect the trivial. However, Eliot noted that the verse plays written in the previous century were often unduly hampered by the lack of "flexibility" in their adherence to strict meter. Therefore, Eliot did not stick to strict meter in writing this verse play. Eliot did, however, like other playwrights of the time, experiment with and borrow from Greek drama, adding a chorus to this play to comment on the action, just as playwrights like Sophocles did in ancient Greece.
The choice of poetic form also points to a salient feature of the play that connects to poetics: it was written primarily for political rather than aesthetic purposes. Form follows function, and Eliot wanted to write in the more "universal" form of poetry in order to emphasize the connectedness between political events in the twelfth century and in the 1930s. The play was specifically commissioned by the Bishop of Chichester to comment on the Night of the Long Knives, a shocking event in 1934 in which Hitler murdered (or "purged") hundreds of his perceived enemies, including former good friends. Eliot wanted to use a serious and high-minded verse style to point to the parallels between the way Henry II turned on his close friend Becket for political reasons and Hitler's cynical betrayal of his own close friends. Eliot hoped people would see these parallels and that the gravity of his poetic forms would emphasize the gravity of the situation in Europe and the need for action.