Possessed of a strong and austere character, she refused the hand of the heir-presumptive, Romanus, who was married instead to her sister Zoë in 1028. Though living in retirement she excited Zoë's jealousy, and on a pretext of conspiracy was confined in a monastery.
In April 19, 1042 the popular movement which caused the dethronement of Michael V also led to Theodora's installment as co-empress with her sister. After two months of active participation in government she allowed herself to be virtually superseded by Zoë's new husband, Constantine IX, on June 11, 1042.
Upon his death on January 11, 1055, and in spite of her seventy years of age, she reasserted her dormant rights with vigour, and frustrated an attempt to supersede her on behalf of the general Nicephorus Bryennius. By her firm administration she controlled the unruly nobles and checked numerous abuses; but she marred her reputation by excessive severity towards private enemies and the undue employment of menials for advisers. She died suddenly on August 31, 1057. Having no children and being the last member of her dynasty, she had chosen one of her favorites as her successor. But Michael VI, not being related to the dynasty that had ruled the Byzantine Empire for a period of 189 years (867 - 1056) was not considered to be a rightful Emperor. This resulted in a series of conflicts for the throne between various noble families that lasted from 1056 till 1081.