In the mid 1880s, Parry was struggling to establish himself as a composer. In 1886 he had been disappointed when his one attempt at opera, Guenever, was rejected by the impresario Carl Rosa. Shortly after that setback, Parry was commissioned by Charles Villiers Stanford to compose a piece for the Bach Choir of London, of which Parry was a member. Stanford, one of the first British musicians to recognise Parry's talent, called him the greatest English composer since Purcell.
Stanford had originally intended to perform an existing work of Parry's, the 1885 cantata The Glories of our Blood and State. As the concert was to mark the Golden Jubilee of Queen Victoria, it was thought that such lines in the text as "Sceptre and crown must tumble down" made the work unsuitable for the occasion. Asked to write a new piece, Parry turned, at the suggestion of his colleague George Grove, to Milton's ode, which he had been considering setting for many years.
The main item in the concert was the first London performance of Hector Berlioz's Te Deum (1849), dedicated to the queen's late husband, Albert, Prince Consort. Berlioz's work is on an enormous scale, and would have overshadowed any companion piece other than one of the highest quality. Reviewing the concert, The Times said of Blest Pair of Sirens:
The choral writing is in eight parts and abounds in contrapuntal devices. At the same time the spirit and the accent of the words are carefully attended to, as befits a work in which "sphere-born harmonious sisters, voice and verse" are invoked to "wed their divine sounds, and mix'd power employ". An excellent rendering contributed to the brilliant success of the ode.
The work was an immediate success, and was quickly taken up by other choirs. The following year it was given alongside Sullivan's The Golden Legend at the Three Choirs Festival. Recognised as "one of the outstanding English choral works", the work has remained a standard in the choral repertory. Among its higher-profile performances in the 21st century were those by BBC forces at the Last Night of the Proms in September 2010, and by the choirs of Westminster Abbey and the Chapel Royal at the wedding of the Duke and Duchess of Cambridge in April 2011.