Since her younger brother Emperor Monmu's son Obito no miko (the future Emperor Shomu) was still young, she ascended the throne as her mother Empress Genmei abdicated.
弟・文武天皇の子である首（おびと）皇子（後の聖武天皇）がまだ若い為、母・元明天皇から譲位を受け即位。