Seumas or Seamus O'Sullivan (born James Sullivan Starkey; 17 July 1879 – 24 March 1958) was an Irish poet and editor of The Dublin Magazine. His father, William Starkey (1836–1918), a physician, was also a poet and a friend of George Sigerson. He was born in Dublin and spent his adult life in the suburb of Rathgar. In 1926, he married the artist Estella Solomons, sister of Bethel Solomons. Her parents were opposed to the marriage as Seumas was not Jewish.
His books include Twilight People (1905), Verses Sacred and Profane (1908), The Earth Lover (1909), Selected Lyrics (1910), Collected Poems (1912), Requiem (1917), Common Adventures (1926), The Lamplighter (1929), Personal Talk (1936), Poems (1938), Collected Poems (1940), and Dublin Poems (1946). Terence de Vere White praised him as "a true poet", and was critical of W. B. Yeats for leaving him out of his anthology of Irish poets, which he thought a particularly strange decision since Yeats and O'Sullivan were friends, although they quarrelled from time to time. In 1936 a version of a play by Irish playwright Teresa Deevy called The King of Spain's Daughter was included in The Dublin Magazine which was edited by O'Sullivan. Moeran also published 'Invitation in autumn' (1943) as a separate song. With its straightforward language and direct imagery, his poetry was attractive to composers, particularly his most popular poem 'The Piper' ('A piper in the streets today') which was set by Peter Crossley-Holland, Michael Head, Ivor Gurney, Norman Peterkin and Vaughan Williams.