During the reign of Queen Elizabeth I, England is concerned by the impending arrival of the Spanish Armada. In 1588, relations between Spain and England are at breaking point. With the support of Queen Elizabeth I (Flora Robson), English privateers such as Sir Francis Drake regularly capture Spanish merchantmen bringing gold from the New World.
Elizabeth's chief advisers are the Lord Treasurer, Lord Burleigh (Morton Selten), and her longtime admirer, Robert Dudley, Earl of Leicester (Leslie Banks). Burleigh's 18-year-old granddaughter Cynthia (Vivien Leigh) is one of Elizabeth's ladies-in-waiting, and the ageing queen is plagued by jealousy of the girl's beauty and vivacity.
In a sea battle between the Spanish, led by Don Miguel (Robert Rendel), and the English, led by his old friend Sir Richard Ingolby (Lyn Harding) the English are captured. Miguel allows Richard's son Michael (Laurence Olivier) to escape. Michael washes ashore on Miguel's estate, and his wounds are tended to by Miguel's daughter Elena (Tamara Desni), who quickly becomes enamoured of the handsome Englishman. As the months pass, Michael recovers and laments being apart from Cynthia, his sweetheart, but is nonetheless impressed by Elena's charms.
Miguel brings Michael the sad news that Sir Richard, his father, has been executed as a heretic. The grieving Michael denounces his rescuers and flees to England in a small fishing boat. When he is granted an audience with the Queen he urges her to fight the Spanish menace by whatever means necessary, and swears undying loyalty to her. Elizabeth is flattered by the young man's fervent devotion and later has an opportunity to take advantage of his offer of service when Hillary Vane (James Mason), an Englishman spying for Spain, is killed before the names of his English co-conspirators can be uncovered.
Michael, disguised as Vane, goes to the court of King Philip II of Spain (Raymond Massey) to get the letters that will set into motion a plan to assassinate Elizabeth. At the palace Michael meets Elena. Her father has been killed by the English and she is now married to Don Pedro (Robert Newton), the palace governor. Elena keeps Michael's identity a secret as long as she can, but finally must tell her husband out of loyalty to him.
Philip sees through Michael's disguise and orders his arrest. Pedro helps him escape so that it will not be discovered that his wife aided a heretic. While Michael is returning home, the Spanish Armada sails against England and Elizabeth addresses her army at Tilbury. Michael meets her there and reveals the names of the traitors. Elizabeth knights Michael before confronting the six traitors, inviting them to fulfill their plot and kill her. Overwhelmed with shame, they agree to accompany Michael on a mission to deploy fire ships in a night attack on the Armada, massed off the coast of England.
The tactic succeeds, and Elizabeth allows Michael and Cynthia to be wed.
With the working title of Glorianna, principal photography took place at Denham Studios, where a large water tank was used to launch the model ships representing the Spanish Armada and the English naval defenders. Originally Conrad Veidt was to star, but Alexander Korda saw the production as a star vehicle for Vivien Leigh, who was under contract to Korda. Along with the historical drama that was portrayed, Fire Over England was also a costume romance that served to showcase Leigh and Olivier, a real-life romantic couple.
A portion of the film, including the beacons being lit on the English coast, and an armor-clad Queen Elizabeth giving a speech to the surrounding soldiers at the start of the Battle of Gravelines was used in the 1939 World War II propaganda documentary The Lion Has Wings. It is used to compare the Spanish invasion attempt to a Nazi invasion, demonstrating how Great Britain has survived against great odds in the past, and would again.
The central theme of the film alludes to a perceived Nazi invasion, even though at the time of the film's release the Phoney War had barely begun, and the Battle of Britain was still months away.
Fire Over England was the first British film to have its U.S. premiere at Los Angeles. Overall, the picture garnered positive reviews. In the review in Variety, the comment was "This is a handsomely mounted and forcefully dramatic glorification of Queen Bess. It holds a succession of brilliantly played scenes, a wealth of choice diction, pointed excerpts from English history and a series of impressive tableaux." The League of Nations Committee on Motion Pictures awarded the 1937 Cinema Medal of Honor to Fire Over England.