The 21-year-old Mozart visited Mannheim in 1777 on a job-hunting tour with his mother and developed a close relationship with the Weber family. He fell in love, not with the 15-year-old Constanze, but with her older sister Aloysia. While Mozart was in Paris, Aloysia obtained a position as a singer in Munich, and the family accompanied her there. She rejected Mozart when he passed through Munich on his way back to Salzburg.
The month after the family moved to Vienna in 1779, again following Aloysia as she pursued her career, her father Fridolin died. By the time Mozart moved to Vienna in 1781, Aloysia had married Joseph Lange, who agreed to help her mother Cäcilia Weber with an annual stipend, and she took in boarders to make ends meet. The house where the Webers lived (on the second floor) was at Am Peter 11, and bore a name (as houses often did at the time): Zum Augen Gottes ("God's Eye").
On first arriving in Vienna on 16 March 1781, Mozart stayed at the house of the Teutonic Order with the staff of his patron, Archbishop Colloredo. In May, he "was obliged to leave," and chose to board in the Weber household, originally intending "to stay there only a week."
After a while, it became apparent to Cäcilia Weber that Mozart was courting Constanze, now 19, and in the interest of propriety, she requested that he leave. Mozart moved out on 5 September to a third-floor room in the Graben.
The courtship continued, not entirely smoothly. Surviving correspondence indicates that Mozart and Constanze briefly broke up in April 1782, over an episode involving jealousy (Constanze had permitted another young man to measure her calves in a parlor game.) Mozart also faced a very difficult task getting his father Leopold's permission for the marriage.
The marriage finally took place in an atmosphere of crisis. Heartz suggests that eventually Constanze moved in with Mozart, which would have placed her in disgrace by the mores of the time. Mozart wrote to Leopold on 31 July 1782, "All the good and well-intentioned advice you have sent fails to address the case of a man who has already gone so far with a maiden. Further postponement is out of the question." Heartz relates, "Constanze's sister Sophie had tearfully declared that her mother would send the police after Constanze if she did not return home (presumably from Mozart's apartment)." On 4 August, Mozart wrote to Baroness von Waldstätten, asking "Can the police here enter anyone's house in this way? Perhaps it is only a ruse of Madame Weber to get her daughter back. If not, I know no better remedy than to marry Constanze tomorrow morning or if possible today."
The marriage did indeed take place that day, 4 August 1782. In the marriage contract, Constanze "assigns to her bridegroom five hundred gulden which [...] the latter has promised to augment with one thousand gulden", with the total "to pass to the survivor". Further, all joint acquisitions during the marriage were to remain the common property of both. A day after the marriage took place, the consent of Wolfgang's father arrived in the mail.
The couple had six children, of whom four did not survive infancy.
* Raimund Leopold (17 June – 19 August 1783)
* Karl Thomas Mozart (21 September 1784 – 31 October 1858)
* Johann Thomas Leopold (18 October – 15 November 1786)
* Theresia Constanzia Adelheid Friedericke Maria Anna (27 December 1787 – 29 June 1788)
* Anna Maria (b/d 25 December 1789)
* Franz Xaver Wolfgang Mozart (26 July 1791 – 29 July 1844)
Mozart died in 1791, leaving debts and placing Constanze in a difficult position. At this point Constanze's business skills came into fruition: she obtained a pension from the Emperor, organized profitable memorial concerts, and embarked on a campaign to publish her husband's works. These efforts eventually made Constanze financially secure.