His son Eduardo Frei Ruiz-Tagle, 1942-, also president of Chile (1994-2000), was a civil engineer and businessman before he helped found (1988) the Committee for Free Elections and campaigned against the extension of Pinochet's term as president. Elected to the senate in 1989, Frei became head of the Christian Democratic party in 1991 and its candidate for president in 1993. Benefiting from his late father's popularity, he was elected handily. The policies of the Aylwin government were largley continued during Frei's term in office. He was succeeded as president by Ricardo Lagos. the first Socialist to hold the office since Allende. Frei failed to win a second presidential term in 2010, losing to conservative businessman Sebastián Piñera.
He began his political career in the Conservative Party, but was among a group of young men who founded their own party in 1938: the Falange Nacional. In 1957, the Falange became the Christian Democratic Party of Chile, and he became the undisputed leader.
He was minister of Public Works in 1945, and senator in 1949. He ran for president in 1958 before being elected in 1964. That year he was elected with his "Revolución en Libertad" ("Revolution in Liberty") slogan by a large margin (56%), defeating Socialist candidate Salvador Allende who only received 39% of the vote, but who subsequently won the 1970 Chilean presidential election.
His campaign had been supported by the CIA, who feared an Allende victory, with US$ 3 million, mostly used in the Chilean media.
Furthermore, in 1966, the Rapa Nui of Easter Island gained full Chilean citizenship. The Easter Island had been annexed in 1888 by Chile. However, until 1953 the Island had been rented to the Williamson-Balfour Company as a sheep-farm, while the surviving Rapanui were confined to the settlement of Hanga Roa and the rest of the island managed by the Chilean Navy, until its opening to the public in 1966.
After Allende's 1970 victory, Frei became convinced of what he called a "totalitarian project" to impose a Communist tyranny. His Christian Democratic Party supported the Armed Forces intervention to remove Allende from office in 1973, after the Chamber of Deputies on August 22, 1973, accused Allende of violating the Constitution. In November 1974 Frei wrote a historic letter to Mariano Rumor, President of the International Christian Democrats, endorsing the Armed Forces intervention and denouncing what he alleged was an attempt by Allende to impose in Chile a Communist dictatorship.
Frei later became part of the opposition against the Augusto Pinochet dictatorship.
His death is a matter of controversy due to allegations that he was poisoned by the Pinochet regime, allegedly using a toxin produced by the DINA biochemist Eugenio Berrios. After Belgian researchers from the University of Ghent reportedly found mustard gas in Frei's body, the former president's family filed a lawsuit, which is still pending as of 2007. Some commentators, notably conservative columnist Hermógenes Pérez de Arce, dispute the existence of the Belgian report, citing the denial by the University's chief of communications, Tom de Smedt, that an investigation had been done in that university.