Wagner is a respected composer based in Dresden where he works as royal court conductor for the King of Saxony. Although his wife, Minna, enjoys their life and status, Wagner is bored with his work for the ageing king and spends most of his time writing revolutionary pamphlets against the establishment and aristocracy. Eventually, the May Uprising breaks out in which Wagner becomes an important figure. When Saxon and Prussian troops crush the uprising, Wagner becomes a wanted man and is forced to flee to Zürich.
After refusing to join her husband for quite some time, Minna eventually agrees to move to Zürich to be reunited with Wagner. She manages to persuade Wagner to start conducting and composing again and urges him to travel to France. In Bordeaux he meets a wealthy Scottish emigree, Mrs Taylor, who agrees to become a patron of his, although he has a brief affair with her married daughter. Upon travelling to Paris, Wagner is ordered to leave the city at once and return to Zürich. In Zürich he meets up with his good friend Franz Liszt, while also taking on a pupil, Karl Ritter, the son of another patron, Mrs Ritter.
Wagner's health deteriorates and he suffers from various illnesses. Mathilde Wesendonck, the wife of wealthy silk merchant Otto Wesendonck, becomes yet another one of his patrons and offers him the cottage on her estate as his residence. Once installed in the cottage, Wagner begins a passionate correspondence with Mathilde, which upsets both Mathilde's husband, Otto, and Wagner's wife, Minna, who seeks solace in increasing amounts of laudanum. Wagner, who starts composing Tristan und Isolde for Mathilde, is also visited by his good friend Hans von Bülow, and his new bride Cosima, Liszt's daughter. After a while, Minna works up the courage to confront Wagner and Mathilde about their correspondence.
Wagner moves to Venice to finish Tristan und Isolde. When Karl Ritter informs him that Mrs Ritter is no longer able to provide Wagner with money, he ends their friendship and travels to Paris. In Paris he is ordered by the French emperor to stage a new version of his famous opera Tannhäuser. However, the show is a fiasco when riots break out during the performance to protest both Wagner's break with artistic conventions (a ballet in the first act, instead of the second) and the involvement of one of his patrons, the Austrian Princess Metternich.
After the failure in Paris, Wagner travels around Europe to Switzerland, Austria and Russia. He tries staging Tristan und Isolde in Vienna, but is unsuccessful. Meanwhile, Minna continues to plead with the Dresden court for amnesty for Richard, which is eventually granted. Wagner returns but is chased away when creditors come looking for him. Destitute, Wagner tries to hide but is eventually found by Pfistermeister, personal secretary to the King of Bavaria who is desperate to meet him.
Wagner enjoys a prosperous time under the patronage of the young King of Bavaria. Most of his debts are settled and several of his operas are staged to great success. Meanwhile, Wagner has an affair with Cosima, wife of his good friend Hans von Bülow, much to the dismay of Cosima's father, Franz Liszt. Although Wagner and King Ludwig II have become close friends, the King's ministers and the people of Bavaria are weary of Wagner. Wagner eventually has a falling out with the King when he asks Ludwig to pay for a portrait of Wagner which is painted as a gift to Ludwig himself.
Wagner must reconcile with the King and eventually does so. Their friendship grows even stronger while Ludwig's minsters are becoming increasingly suspicious of Wagner and his ever-increasing demands for money. The premiere of Tristan und Isolde has to be postponed when the lead actress falls ill but finally happens a few months later. Ludwig leaves the premiere before the end to travel into the night on board the royal train. When Bavaria faces external challenges and Wagner's lifestyle becomes too extravagant for the Bavarian people, Ludwig is finally forced to banish Wagner from his country. Meanwhile, Cosima gives birth to Wagner's daughter, while Minna dies alone, neglected by Wagner.
Wagner moves to Lucerne with Cosima and her children. He is later joined by King Ludwig who wishes to abdicate in order to become Wagner's assistant. Wagner convinces him to return to Bavaria, where war with Prussia erupts. Hans von Bülow eventually also visits them in Lucerne, where Cosima asks him for a divorce, which he refuses. When Hans is overly tired by his work for Wagner, he leaves, and Wagner hires Hans Richter as his new assistant. They are visited by Friedrich Nietzsche. Cosima gives birth to Wagner's son.
Wagner and Cosima are overjoyed by the birth of their son, Siegfried. Meanwhile, Germany continues its war with France, which finally realises Wagner's lifelong dream of a united Germany. Wagner marries Cosima and is ordered by Ludwig to stage his opera Das Rheingold. When Wagner decides to postpone the opera, one day before the premiere, he and Ludwig have a falling out. Wagner is denied access to the theatre and decides to build his own opera house in Bayreuth.
Construction on the opera house in Bayreuth begins and his epic Der Ring des Nibelungen can finally be premiered. The performance is attended by Ludwig who is slowly losing his mind, while living in his gigantic new castle Neuschwanstein. Wagner and Nietzsche have a falling out over Wagner's lifestyle and ideas (including his rampant anti-semitism). Shortly before his death, Wagner and Liszt reflect on Wagner's life: the people he has known, the events that occurred and the music he composed.