Obiang's first assignment was as a territorial guard. He was soon promoted to the rank of lieutenant. As the nephew of then-President Macías Nguema, Obiang was given several important positions and promotions. He served as the military governor of Fernando Po and as director of the Playa Negra prison. In 1975, he was promoted to lieutenant colonel and became Nguema's aide-de-camp, a position he held until ousting his uncle from power.
In the spring of 1979, Macías Nguema had Obiang's brother executed. Obiang reportedly began planning his uncle's overthrow at this time. He evacuated his family and on 3 August 1979 set into motion the coup d'état that would place him in power.