Princess Märtha Louise was born on 22 September 1971 in Oslo to the then Crown Prince Harald and Crown Princess Sonja. At birth, she was not in line to the throne, because until 1990, only males could inherit the Norwegian throne (Salic law). She was christened a few months after her birth. Her godparents are King Olav V of Norway, Princess Margaretha of Sweden, Count Flemming of Rosenborg, Princess Ragnhild of Norway, Dagny Haraldsen, Haakon Haraldsen, Nils Jørgen Astrup and Ilmi Riddervold.
In 1973, Märtha Louise was joined by a younger brother Haakon Magnus. In 1990 the Norwegian constitution was altered, granting full cognatic primogeniture to the Norwegian throne, meaning that the eldest child, regardless of gender, takes precedence in the line of succession. This change only affects those born in 1990 or later. Females born between 1971 and 1990 (i.e. only Märtha Louise), were given succession rights, but their brothers would be before them in the line of succession, meaning that Prince Haakon still took precedence over Märtha Louise in the line of succession.
After the births of her brother’s two children, Ingrid Alexandra and Sverre Magnus, Märtha Louise was relegated to fourth in line. The princess is also 73rd in the line of succession to the throne of each of the sixteen Commonwealth Realms, as a great-great-granddaughter of King Edward VII.