In 1853, Princess Sophie of Bavaria, the domineering mother of 23-year-old Emperor Franz Joseph, preferring to have a niece as a daughter-in-law rather than a stranger, arranged a marriage between her son and her sister Ludovika's eldest daughter, Helene. Although the couple had never met, Franz Joseph's obedience was taken for granted by the archduchess, who once was described as "the only man in the Hofburg" for her authoritarian manner. The Duchess and Helene were invited to journey to the resort of Bad Ischl, Upper Austria to receive his formal proposal of marriage. Fifteen-year-old Sisi accompanied her mother and sister and they traveled from Munich in several coaches. They arrived late as the Duchess, prone to migraine, had to interrupt the journey and the coach with their gala dresses never did arrive. The family was still in mourning over the death of an aunt so they were dressed in black and unable to change to more suitable clothing before meeting the young Emperor. While black did not suit eighteen-year-old Helene's dark coloring, it made her younger sister's blonder looks more striking by contrast.
Helene was a pious, quiet young woman, and she and Franz Joseph felt ill at ease in each other's company, but Franz Joseph was instantly infatuated with Elisabeth. He did not propose to Helene, but defied his mother and informed her that if he could not have Elisabeth, he would not marry at all. Five days later their betrothal was officially announced. The couple were married eight months later in Vienna at the Augustinerkirche on 24 April 1854.