By 1952, the González Videla government was on its last legs, weakened by corruption scandals. The Chilean Socialist Party was in the process of nominating Salvador Allende as its candidate for the September 1952 presidential elections and was keen to have the presence of Neruda, by now Chile's most prominent left-wing literary figure, to support the campaign. Neruda returned to Chile in August of that year and rejoined Delia del Carril, who had traveled ahead of him some months earlier, but the marriage was crumbling. Del Carril eventually learned of his affair with Matilde Urrutia and he sent her back to Chile in 1955. She convinced the Chilean officials to lift his arrest, allowing Urrutia and Neruda to go to Capri, Italy. Now united with Urrutia, Neruda would, aside from many foreign trips and a stint as Allende's ambassador to France from 1970 to 1973, spend the rest of his life in Chile.
By this time, Neruda enjoyed worldwide fame as a poet, and his books were being translated into virtually all the major languages of the world. He vigorously denounced the United States during the Cuban Missile Crisis and later in the decade he likewise repeatedly condemned the U.S. for its involvement in the Vietnam War. But being one of the most prestigious and outspoken left-wing intellectuals alive, he also attracted opposition from ideological opponents. The Congress for Cultural Freedom, an anti-communist organization covertly established and funded by the U.S. Central Intelligence Agency, adopted Neruda as one of its primary targets and launched a campaign to undermine his reputation, reviving the old claim that he had been an accomplice in the attack on Leon Trotsky in Mexico City in 1940. The campaign became more intense when it became known that Neruda was a candidate for the 1964 Nobel Prize, which was eventually awarded to Jean-Paul Sartre (who rejected it).
In 1966, Neruda was invited to attend an International PEN conference in New York City. Officially, he was barred from entering the U.S. because he was a communist, but the conference organizer, playwright Arthur Miller, eventually prevailed upon the Johnson Administration to grant Neruda a visa. Neruda gave readings to packed halls, and even recorded some poems for the Library of Congress. Miller later opined that Neruda's adherence to his communist ideals of the 1930s was a result of his protracted exclusion from "bourgeois society". Due to the presence of many Eastern Bloc writers, Mexican writer Carlos Fuentes later wrote that the PEN conference marked a "beginning of the end" of the Cold War.
Upon Neruda's return to Chile, he stopped in Peru, where he gave readings to enthusiastic crowds in Lima and Arequipa and was received by President Fernando Belaúnde Terry. However, this visit also prompted an unpleasant backlash; because the Peruvian government had come out against the government of Fidel Castro in Cuba, July 1966 saw more than one hundred Cuban intellectuals retaliate against the poet by signing a letter that charged Neruda with colluding with the enemy, calling him an example of the "tepid, pro-Yankee revisionism" then prevalent in Latin America. The affair was particularly painful for Neruda because of his previous outspoken support for the Cuban revolution, and he never visited the island again, even after receiving an invitation in 1968.
After the death of Che Guevara in Bolivia in 1967, Neruda wrote several articles regretting the loss of a "great hero". At the same time, he told his friend Aida Figueroa not to cry for Che, but for Luis Emilio Recabarren, the father of the Chilean communist movement, who preached a pacifist revolution over Che's violent ways.