The Grub Street Opera is a play by Henry Fielding that originated as an expanded version of his play The Welsh Opera. It was never put on for an audience and is Fielding's single print-only play. As in The Welsh Opera, the author of the play is identified as Scriblerus Secundus. Secundus also appears in the play and speaks of his role in composing the plays. In The Grub Street Opera the main storyline involves two men and their rival pursuit of women.
The play is Fielding's first truly political play and first ballad opera. Unlike The Welsh Opera, the play deals with morality from the beginning. Additionally, it linked to Fielding's previous attacks on the London theatre and inept writers. Fielding also used the virtue of female servants as a point of humour and to discuss morality, while using the effeminacy and dominance by women to mock various characters and discuss the issue of gender roles. Critics viewed The Grub Street Opera positively, noting it to be a definite improvement on The Welsh Opera.
Fielding created three theatrical versions of The Grub Street Opera. Of these, one was performed at a Haymarket theatre, but only in rehearsals. The play originates as an expanded version of The Welsh Opera. The revision had a puff piece in the 21 May 1731 Daily Post saying, "We hear that the Grubstreet Opera, written by Scriblerus Secundus, which was to have been postponed till next Season, will, at the particular Request of several Persons of Quality, be perform'd within a Fortnight, being now in Rehearsal at the New Theatre in the Hay-market."
Later, it was advertised again in the 5 June 1731 Daily Post as being rehearsed, but the 11 June edition stated that one of the performers was sick and the 14 June edition said that the play would be postponed indefinitely. It was never produced, and The Grub-Street Opera is the only play by Fielding that existed only as a printed play. It is unknown as to why the play was never put on for an audience, but it is possible that it was not performed because Fielding was either legally prevented to perform it by the British government or he was bribed to not perform it.John Henley, a defender of Robert Walpole and Walpole's government, discussed the incident in his poem "Hay-Market Actors of the design'd Grub-street Opera" (published in the 8–15 June 1731 edition of his newspaper, Hyp-Doctor). In it, he gloated over the play being kept from performance and stated that the government did not accept the play. He followed this in the 15–22 June edition with an attack upon Fielding.