An elderly Antonio Salieri confesses to the murder of his former colleague, Wolfgang Amadeus Mozart, and attempts to kill himself by slitting his throat. Two servants take him to a sanatorium where a priest, Father Vogler, implores him to confess.
Salieri recounts how, even in his youth, he desired to be a composer, much to the chagrin of his father. He prays to God that, if he will make Salieri a famous composer, he will in return promise his faithfulness. Soon after, his father dies, which Salieri takes as a sign that God has accepted his vow. He is educated in Vienna and becomes court composer to Emperor Joseph II.
Mozart arrives in Vienna to perform at the request of his employer, the Prince-Archbishop of Salzburg. Salieri attends the performance to meet Mozart and, despite Mozart’s obscenity and immaturity, finds his talent to be transcendent.
The Emperor desires to commission Mozart to write an opera and, despite the reservations of his advisers, summons him to the palace. Mozart happily accepts the job, much to the annoyance of Salieri. Mozart premieres Die Entführung aus dem Serail to mixed reviews from the Emperor. Salieri believes that Mozart has slept with the star, Caterina Cavalieri, despite his engagement to Constanze Weber.
The Emperor desires that Mozart instruct his niece, Princess Elisabeth, in music, but Salieri discourages him from doing so. Constanze visits Salieri to persuade him to make the Emperor reconsider, but she is unsuccessful.
Salieri is enraged that God has bestowed upon Mozart the talent he has so desperately desired and vows to destroy Mozart. Mozart, meanwhile, struggles to find work and begins drinking. His father, Leopold Mozart, comes to visit him in Vienna. Constanze and Mozart take Leopold to a masked party (which Salieri also attends), where Mozart entertains the guests with musical antics. Leopold disapproves of his son’s hedonism, and the family argues until Leopold leaves town.
Salieri hires a young girl to pose as the Mozarts’ maid while spying for him. She takes him to the Mozart residence, where he discovers that Mozart is working on an opera based on the play The Marriage of Figaro, which the Emperor has forbidden. When Mozart is summoned to court to explain, he manages to convince the Emperor to allow his opera to premiere, despite Salieri and the advisers’ attempts at sabotage.
Messengers arrive in Vienna with news of Leopold’s death, and in response a grief-stricken Mozart pens Don Giovanni. Salieri recognizes the dead commander as symbolic of Leopold and hatches a plan. Wearing Leopold’s party mask, Salieri visits Mozart and commissions a Requiem Mass. Salieri plots to kill Mozart once the piece is finished, then premiere it at Mozart’s funeral, claiming the work as his own.
At a parody of one of Mozart’s own operas, Emanuel Schikaneder asks Mozart to write an opera for his theater. Mozart, desperate for money, obliges, despite Constanze’s insistence that he finish the Requiem Mass. The couple fight and Constanze leaves with their young son, Karl.
Mozart collapses during a performance of his finished work, The Magic Flute. Salieri takes him home and offers his assistance on the Requiem. Salieri transcribes Mozart’s verbal direction, and they work through the night. The next morning, a gravely ill Mozart apologizes to Salieri for his previous behavior. A guilty Constanze returns home and locks the unfinished Requiem away, only to find that Mozart has died from overwork. Mozart is taken out of the city and unceremoniously buried in a mass grave during a rainstorm. His mourners, daunted by the weather, watch from the city gate as the coffin is taken away.
Having finished his tale, Salieri asks how a merciful God could destroy his own beloved just to keep a mediocrity like Salieri from sharing in his glory. As he is pushed down the hall of the sanatorium in a wheelchair, Salieri declares himself “the patron saint of mediocrities” and mockingly absolves the other patients of their inadequacies. Mozart’s high-pitched laugh is heard as the screen fades to black.