Maria Theresa's father died in 1744.
Maria Theresa Walburga Amalia Christina ( Maria Theresia [ maˈʁiːa teˈʁeːzi̯a ] 13 May 1717 -- 29 November 1780 ) was the only female ruler of the Habsburg dominions and the last of the House of Habsburg . She started her 40-year reign when her father , Emperor Charles VI , died in October 1740 . Upon the death of her father , Saxony , Prussia , Bavaria , and France all repudiated the sanction they had recognised during his lifetime .