Following the assassination of his father, Anastasio Somoza García, Luis was tapped as acting president and was elected president in his own right later that year. His rule was somewhat milder than that of his father. He blocked reelections for a second term for fairness to others. However, civil liberties remained restricted and corruption remained widespread.
His brother, Anastasio Somoza Debayle, headed the National Guard and was the second most powerful man in the country during his older brother's rule. Using his position as head of the Guard, he saw to it that the presidency was held from 1963 onward by politicians loyal to his family. As a result, Luis remained the real power in Nicaragua until his death in 1967 from a massive heart attack at the age of 45 in Managua. Under Luis Somoza's regime, Nicaragua was a key player in the ushering of the creation of the Central American Common Market, with the Alliance for Progress backing that common market's creation. During the Bay of Pigs Invasion, he allowed the CIA-trained Cuban rebels to embark from Puerto Cabezas, on Nicaragua's Caribbean coast. The Sandinistas began their struggle against the government in 1963--a struggle that would topple his brother in 1979.
He is entombed at Cementerio Occidental with his father in the National Guard Mausoleum in Managua, Nicaragua.
He was a member of Fi Sigma Alfa Fraternity.