The party was a spin-off of the Civic Union, which was led by Bartolomé Mitre and Leandro Alem The party unsuccessfully led an attempt to force the early departure of President Miguel Juárez Celman in the Revolution of the Park (Revolución del Parque). Eventually a compromise was reached with Juárez Celman's government. Hard-liners who opposed this agreement founded the current UCR, led by Alem's nephew, the young and charismatic Hipólito Yrigoyen. In 1893 and 1905 the party led unsuccessful revolutions to overthrow the government. With the introduction of free, fair and secret elections based on universal suffrage in 1912 the Party managed to win the general elections of 1916, when Hipólito Yrigoyen became president. The Radical Civic Union remained in power during the next 14 years: Yrigoyen was succeeded by Marcelo T. de Alvear in 1922 and by himself in 1928. The first coup in Argentina's modern history occurred on September 6, 1930 and ousted an aging Yrigoyen amid an economic crisis resulting from the United States' Great Depression.
From 1930 to 1958 the Radical Civic Union was confined to be the main opposition party, either to the Conservatives and the military during the 1930s and the early 1940s or to the Peronism during the late 1940s - early 1950s. It was only in 1958 when a faction of the party allied with banned peronists (the so called Intransigent Radical Civic Union) came back to power, led by Arturo Frondizi. The growing tolerance of Frondizi towards its peronist allies provoked unrest in the army, which ousted the president in March 1962. After a brief military government, presidential elections took place in 1963 with the Peronist Party banned (as in 1958). The outcome of the elections saw the candidate of the People's Radical Civic Union (the other party's faction) Arturo Illia coming in the first place but with only 25% of the votes (approximately 19% of the votes were blank due to the peronism's banning). Although Argentina witnessed during Illia's presidency one of the best economic performances in its history, the president was ousted by the army in June 1966. Illia's peaceful and ordered style of governing - sometimes considered too "slow" and "boring" - was being heavily criticized at the time.
During the 1970s peronist government (1973-1976), the Radical Civic Union was the second most voted party, but this didn't actually grant the party the role of being the political opposition. In fact, the peronist government's most important criticisms came from the same Peronist Party (now called Justicialist Party). The UCR's leader in those times, Ricardo Balbín, saluted Peron's coffin (Perón had died on July 1, 1974, during his third mandate as president) with the famous sentence "This old adversary salutes a great friend", thus marking the end of the peronist-radical rivalry that had marked the pace of the Argentine political scene until then. The growing fight between left-wing and right-wing peronists took the country into chaos and many UCR members were targeted by both factions. The subsequent coup in 1976 ended the peronist experience and "disappeared" many members of the UCR party as well.
Between 1983 and 1989 its leader, Raúl Alfonsín, was the first democratically elected president after the military dictatorship headed by generals such as Jorge Videla, Leopoldo Galtieri and Reynaldo Bignone. Alfonsín was succeeded by Carlos Menem of the Peronist Justicialist Party (PJ).
In 1997 the UCR participated in elections in coalition with Front for a Country in Solidarity (FREPASO), itself an alliance of many smaller parties. This strategy brought Fernando de la Rúa to the presidency in the 1999 elections. During major riots triggered by economic reforms implemented by the UCR government (with the advice of the International Monetary Fund), President de la Rúa resigned and fled the country to prevent further turmoil. After three consecutive acting presidents assumed duties in the following weeks, Eduardo Duhalde of the PJ took office until new elections could be held.
After the 2001 legislative elections it became the second largest party in the federal Chamber of Deputies, winning 71 of 257 seats. It campaigned in an alliance with the smaller, more leftist FREPASO. The party has subsequently declined markedly and its candidate for President in 2003 gained just 2.34% of the vote, beaten by three Peronists and more seriously, by two former radicals, Ricardo López Murphy of Recrear and Elisa Carrió of ARI, who have leached members, support and profile from the UCR. In the 2005 legislative elections, the UCR was reduced to 35 deputies and 13 senators, but remains the second force in Argentine politics.
Ahead of the 2007 election, the remaining Radicals divided between those who wanted to find an internal candidate and those who wanted to back a candidate from another movement, mostly former Economy Minister Roberto Lavagna, supported by former president Raúl Alfonsín.
In May 2005, the National Committee of the UCR, then led by Ángel Rozas, intervened (suspended of authorities of) the Provincial Committee of the UCR in Tierra del Fuego Province after Radical governor Jorge Colazo spoke in favour of Kirchner's reelection. The intervention was rejected by the Provincial Committee.
A party convention held in Rosario in August 2006 officially rejected the possibility of alliances with Kirchner's faction of Justicialism and granted former Party President Roberto Iglesias the permission to negotiate with other political forces. This led to several months of talks with Lavagna.
The continued dissidence of the Radicales K prompted the intervention of the UCR Provincial Committee of Mendoza on 1 November 2006, due to the public support of President Kirchner by Mendoza's governor, the Radical Julio Cobos. The measure was short-lived, as the Mendoza Province Electoral Justice overturned it three days later. Deputy and UCR National Committee Secretary General Margarita Stolbizer stated that the party is virtually "broken due to the stance of the leaders who support the alliance [with Kirchner]".
Roberto Iglesias eventually resigned the presidency of the party in November 2006 due to differences with Lavagna, having reached the conclusion that an alliance with him would be a mistake, and joined Stolbizer's camp, maintaining that the party should look for its own candidate (the so-called Radicales R). On 1 December 2006 the National Committee appointed Jujuy Province Senator Gerardo Morales as its new president. Morales stated that he wanted to follow the mandate of the Rosario convention (that is, looking for a possible alliance with Roberto Lavagna).
Morales went on to become Lavagna's running mate in the presidential election of October 2007, coming third. Although this campaign represented the mainstream of the national UCR leadership, substantial elements backed other candidates, notably the Radicales K. Cobos was elected Vice President as the running mate of Cristina Fernández de Kirchner and several Radicals were elected to Congress as part of the Kirchners' Front for Victory faction. The official UCR ranks in Congress were reduced to 30 in the Argentine Chamber of Deputies and 10 in the Argentine Senate.
In Santa Fe, the UCR has teamed up with the Socialist Party to support Socialist candidate for governor Hermes Binner, in exchange for the vice-governorship. Binner has ignored the candidate proposed by the UCR's leadership and is courting the UCR's bases and municipal governments. The UCR is currently debating whether to break the alliance or submit to the Socialists' requirements that the vice-governor be from Santa Fe City and (if possible) a woman.