The King of Germany, Heinrich der Vogler arrives in great pomp in the land of the Brabant to muster forces to counter the invading Hungarians. He unexpectedly ends up mitigating the innocence of Elsa von Brabant, who has been accused by Friedrich von Telramund for the murder of her own brother, the Duke of Brabant.
Friedrich in turn had been deceived by the evil tongued woman Ortrud to believe that Elsa was guilty. Nevertheless, in greed and ugly ambition, Friedrich had married Ortrud to gain leadership of the Brabant, since she is the last surviving Rabod (a ruling family in Brabant). By condemning Elsa to fratricide, he claims ownership of the land, since he has become next in line to the Duke.
An unknown knight, Lohengrin, arrives in a boat drawn by a swan and promises to fight on behalf of Elsa in a battle for honour and truth. Before the fight, Lohengrin begs Elsa to promise never to question his origin and name. Elsa agrees. Expectedly, Lohengrin wins the fight and Friedrich is banished in dishonour.
Through a complicated series of plots, Friedrich and Ortrud both attempt to waggle the steadfast love that Elsa and Lohengrin bear for each other. All their plots to make Elsa question her hero's name fail and eventually results in the death of Friedrich. Nevertheless, thrown into great confusion, Elsa is finally tempted into questioning the origin of Lohengrin in their bridal chamber. Greatly angst-ridden and without option, Lohengrin reluctantly agrees to announce his identity the next day in the presence of the King.
In the morning, amidst great excitement, he announces that he is Lohengrin, son of the Grail King Parzival and that as a Knight of the Grail, he has been sent to combat evil and defend virtue. Further, Knights of the Grail are vested with a power that will be lost when their name is revealed. Neither the King, who is anxious about the imminent battle, nor Elsa his beloved, is able to persuade him to stay - as no one may look upon the grace of the Grail Knights after they reveal their identity. The swan now arrives to take Lohengrin back to the Grail.
Before leaving, Lohengrin prophesies that the King will be victorious and further reveals that it is Ortrud's evil spell that has condemned Elsa's brother, Gottfried, to the form of the swan. He then kneels in prayer and a dove descends from above and hovers about him. The swan sinks into the water and in this instant reverts to the form of Gottfried. Ortrud collapses at the sight of Gottfried. Lohengrin leaves in a boat drawn by the dove, after declaring Gottfried the new ruler of Brabant.