Sumsion's compositional style reflects the influence of his more famous contemporaries Howells, Finzi, and Vaughan Williams, while at the same time retaining something of the 'diatonic strength' of Edwardian composers like Parry and Brewer. Despite these influences, however, Sumsion's music speaks in a fresh and distinctive voice that is appealing to both performers and listeners. His harmonic language is sturdy and conventional, yet often tinged with modality, and his melodic style is fluid and elegant. In the organ and choral works Sumsion displays a fondness for parallel thirds in the accompaniment, detached bass lines, and the descending minor third in the melody.