Mayor

Romero was one of the founding members of the New Progressive Party in 1967. The following year he was elected Mayor of San Juan, Puerto Rico, succeeding the legendary "doña Fela" (Felisa Rincón de Gautier) and becoming the first popularly elected mayor of San Juan, since previous mayors were elected by the San Juan City Council, not directly by the electorate. During his second term, in 1973, he became the first Hispanic to become vice-president of the National League of Cities and in 1974 became president of the organization. He served as mayor until 1976 when he defeated incumbent governor of Puerto Rico Rafael Hernández Colón. While Hernán Padilla was elected to succeed him, technically, his immediate successor was Carlos S. Quirós, his Vice Mayor who became full mayor for over a week until Padilla's term began. Some of his notable accomplishments as mayor were the inclusion of San Juan into U.S. President Lyndon Johnson's Model Cities Program, which changed the face of the slum called "El Fanguito" to become the area of the "new" San Juan where modern facilities such as the San Juan Natatorium, the Puerto Rico Coliseum and numerous residential condominium projects were eventually built; the construction of the Roberto Clemente Coliseum and the first municipal educational institution of Puerto Rico: the Colegio Universitario de San Juan.

Governor

Romero Barceló brought well-received economic resolutions to the island during his terms in office, emphasizing the island's tourism potential. However, during his administration the economy recovered sluggishly, with unemployment dropping to 17% in 1979 from 19.0% in 1975, a disappointing 2% decline. The economy did not fully recover, and the island's government services deteriorated during his term in office. Moreover, his statements declaring the policemen that carried out the Maravilla murders to be heroes damaged his image.^{[citation needed]}

In 1980 he was elected for a second term as governor by a margin of 3,037 votes again over PPD-candidate Rafael Hernández Colón. The 1980 gubernatorial elections were among the closest in Puerto Rican history, requiring the intervention of the Supreme Court of Puerto Rico to rule whether improperly cast ballots should be counted. In particular, the Puerto Rico Statehood Students Association under Luis Fortuño generated over 1,500 absentee ballots for Romero Barceló that proved an important factor in his re-election. However, the New Progressive Party lost control of the legislature, and party-affiliated mayors won in only 28 of the 78 municipalities on the island. The 1980 elections were the most controversial as many PPD followers said that the elections were stolen in which the PPD won the elections except for the governor candidacy in which almost every election the parties win with straight-party ballots. This election was similar to the 2004 and 2012 elections, decided by less-than-one-percent margins.

In his second term Puerto Rico was badly hit by a severe recession starting in 1980 and ending in 1983, the unemployment drastically rose to 25% in 1983 the highest since the Great Depression.

Romero Barceló is frequently associated with the "Cerro Maravilla Incident" of 1978 in which two young pro-Independence activists at Cerro Maravilla were killed at the hands of rogue members of the Puerto Rican Police after being lured by the police to a mountainous area that housed communications and television towers. The tragic incident was investigated several times by the Puerto Rico Justice Department, the U.S. Justice Department, and the F.B.I., and was widely reported on by the local press. In 1984, 10 police officers were indicted and found guilty of perjury, destruction of evidence, and obstruction of justice, with four being convicted of second-degree murder.^[8]

He sought re-election for a third term in 1984 but was defeated by Rafael Hernández Colón. After the elections, Romero-Barceló's reaction to the defeat, in response to TV news reporter Rafael Bracero, was ¿Derrota, qué Derrota? (Defeat, what defeat?). For him, he said, what had occurred was not a defeat, but simply an "electoral loss". The comment has become legendary in Puerto Rican politics.^[9]

Senator

In 1986, he was elected by his party to fill a vacancy in the Senate of Puerto Rico, a position for which he did not seek re-election in 1988. Instead, he returned to his private law practice and shortly thereafter merged his law firm with Del Toro & Santana where he practiced until his election to the United States Congress in 1992.

Resident Commissioner

In the 1992 elections, Romero was elected to the 103rd and 104th United States Congress as Resident Commissioner of Puerto Rico, and relocated to Washington, D.C. He was re-elected to the 105th and 106th United States Congress as well.

During his tenure as Resident Commissioner he campaigned for Puerto Rican statehood, successfully proposed to Congress the derogation of the 936 tax code and endorsed the Young Project, which sought to call a referendum to resolve Puerto Rico's political status. In 2000, he sought a third term but was defeated by PPD's Aníbal Acevedo Vilá. He once again sought his party's nomination for the post of Resident Commissioner in 2003, but was defeated by Luis Fortuño. Although he retired from electoral politics, he remained active in PNP political gatherings, the Puerto Rico Democratic Party, the United States Democratic party, and was a member of the League of United Latin American Citizens.

Shadow United States Senator

On July 3, 2017, he was appointed by Governor Ricardo Rosselló as Puerto Rico's first United States Shadow Senator to the U.S. Senate under the Tennessee Plan approved by Act No. 30 of June 5, 2017 of the Puerto Rico Legislature. Holders of this position do not officially participate in Senate proceedings, but may serve as an advocate for their territories.^[10]