SÃO PAULO, Brazil — Former President Juan María Bordaberry of Uruguay, who as president participated in a coup in 1973 that ushered in a 12-year military dictatorship, died Sunday in Montevideo. He was 83.

His death was announced by his son Pedro.

Mr. Bordaberry had been serving a 30-year sentence under house arrest for orchestrating the coup and for crimes against humanity. He was found guilty of 14 deaths and disappearances related to the dictatorship.

His years as president, between 1971 and 1976, are remembered as perhaps the bleakest in Uruguay’s history, marked by a wave of disappearances, torture and killings intended to wipe out the remnants of the leftist Tupamaro guerrilla movement....