The constitutional court of Guatemala has barred Zury Ríos, the daughter of ex-military ruler Efraín Ríos Montt, from running for the presidency.
Ms Ríos was one of the frontrunners ahead of elections on 16 June.
The court argued that Guatemala's constitution bars close relatives of coup leaders from serving as president.
Efraín Ríos Montt's rule in the 1980s is considered one of the most ruthless periods of Guatemala's civil war, when entire Mayan villages were wiped out.
Gen Rios Montt seized power during a 1982 coup d'état, in the midst of a war between the military regime and Marxist rebels. He was accused of ordering the killing of more than 1,700 ethnic Mayans, whom his regime suspected of harbouring insurgents.
The general was ousted by his defence minister in August 1983 and 30 years later he became the first former head of state to face genocide charges in his own country.
He was found guilty but that ruling was later thrown out by Guatemala's high court. He died aged 91 on 1 April 2018, six months after his genocide trial had resumed.
His daughter Zury Ríos was the right-wing candidate for the Valor (Courage) party.
Relatives of victims of the hundreds of thousands of mainly indigenous people killed during Guatemala's civil war welcomed the court's decision to bar Ms Ríos.
Ms Ríos had earlier said that a bar would not only impinge on her rights to stand as a candidate but also on those of her supporters who want to cast their votes for her.
Polls had placed her among the top three candidates. Her main rivals are former first lady Sandra Torres and the former attorney general, Thelma Aldana.
Both Ms Torres and Ms Aldana face a potential bar from running themselves.
Ms Aldana is facing charges of embezzlement, lying and tax fraud, which she says are politically motivated. Ms Torres is under investigation for alleged illicit campaign funding, which she denies.
The constitutional court is expected to make a decision in both their cases within the next few days.