Galán was born on 29 September 1943 in the city of Bucaramanga, Santander, northeastern Colombia. He had a happy childhood, with strong family bonds, affectionate and sometimes austere, as he had 12 siblings. His father moved with the whole family to Bogotá in 1949.

In Bogotá, Galán attended middle school in the Colegio Americano in 1950. While a student there and only 8 years old, he joined a rally against Conservative president Laureano Gómez and intended to support the Liberal guerrillas. Two years later he was transferred to another school, the Colegio Antonio Nariño. When he was only a 14-year-old, Galán participated in the students protests of 1957 against the dictatorial regime of Gustavo Rojas getting arrested and spending the night in a jail despite his age. In 1960 Galán graduated from high school with honors and began studies of law and economics in the Pontifical Xavierian University in Bogotá, it was then that his liberal radicalism cooled off. While a student in 1963, Galán founded Vértice, a university focused magazine to express his Liberal tendencies in a university that was predominantly Conservative and also became his first experience with journalism. He was able to meet prominent Colombian leaders like former Liberal president Carlos Lleras (who delighted with Galán’s work, decided to write articles for Vértice Magazine) and Colombia’s main circulation newspaper El Tiempo owner and also former Liberal president of Colombia Eduardo Santos during an interview in which Santos was impressed by Galán’s journalist qualities. Galán began working for the Colombian newspaper El Tiempo in 1965 after graduating from university the same year.

In 1970 Galán was appointed Minister of National Education during the presidency of Misael Pastrana. His time as minister was marked by his progressive and social policies, but was not considered successful. In 1972 Galán was appointed Ambassador of Colombia to Italy and later in 1974 while still ambassador, was appointed Colombian representative to the Food and Agriculture Organization of the United Nations (FAO). Under the influence of former president Lleras and after directing the Nueva Frontera Magazine for seven years, in 1976 Galán ran for councilman in the small town of Oiba in the northeastern department of Santander. In 1977 and 1978 Galán became very active and supportive of Carlos Lleras reelection as president of Colombia while he ran for the Senate. The reelection never occurred, however, he got elected as Senator of Colombia representing the Santander Department.

Son of Mario Galán Gómez and Cecilia Sarmiento Suárez, Galán was one of their 12 children, the others being: María Lucía, Gabriel, Cecilia, Helena, Elsa, Gloria, Antonio, Juan Daniel, Mario Augusto, Francisco Alberto and María Victoria Galán Sarmiento. He was cousin of former Attorney General of Colombia Alfonso Valdivieso Sarmiento. In 1971 he married journalist Gloria Pachón Castro and had three children Juan Manuel, Claudio Mario and Carlos Fernando.

In El Tiempo Galán turned himself into a well known journalist and columnist, effort that earned him the director’s assistant position and later the membership of the Executive Directorate in the newspaper with the support of Eduardo Santos and then director Roberto García Peña. He was also active with the Nueva Frontera weekly magazine founded by former president Carlos Lleras, which he directed in 1976 after arriving from Italy. As a journalist Galán wrote no less than 150 editorial articles, followed by other 150 during his time in El Tiempo newspaper.

In 1977 Galán wrote in one of Nueva Frontera’s editorial an article denouncing the existence of narcotics trafficking mafias and that they were influencing the social structure of Colombia. He also denounced the clientelist politics, moral values corruption and collective values loss, this seen as a premonition for Colombia’s future.

On 30 November 1979 Galán founded a party with the name Nuevo Liberalismo and within the Liberal Party.

In 1980 Galán was elected as councilman for the capital, Bogotá to be named the following year, in 1981 as possible candidate for the presidency of Colombia amid divisions in the Liberal Party that intended to challenge the majorities of the party led by Alfonso López Michelsen and then president Julio César Turbay, but voters leaned for the conservative candidate Belisario Betancur. For Galán it had been a positive outcome despite losing, his party Nuevo Liberalismo had gained a 10% of the total votes winning 21 of the 23 Department Assemblies and getting reelected as Senator but he had been criticised by the Liberal Party for creating divisions among them and indeed losing the Presidency.

In 1982 Medellin cartel boss Pablo Escobar tried to infiltrate Galán’s Nuevo Liberalismo Party. Galán publicly rejected him in front of thousands of his fellow men from Antioquia and Colombia.

In 1986 as an anecdote, Galán wrote his autobiography under the pseudonym “Cleo Tilde”, but it was only until 1994 that the identity was revealed. He described detailed facts, events and encounters with prominent figures as well as an approach to his personal point of view and thoughts.

It was only until the mediation of former president Julio César Turbay that Galán returned to the party in 1987 and intended to win the party nomination for official candidate. Galán was growing impatient with the violence and the corruption the drug cartels led by Pablo Escobar and Gonzalo Rodríguez were imposing in Colombia, which encouraged him to try to support the weakening government by shifting the balance of power away from his dangerous enemies.

The Nuevo Liberalism joined the government and was given the Ministry of Agriculture headed by Gabriel Rosas Vega and the Liberal Party gained a solid union that consolidated further when Galán won the Liberal Party’s popular nomination to be the presidential frontrunner. Galán was becoming popular for his open criticism and denunciation of drug cartel violence, he had promised to extradite drug dealers to the United States. He announced he would run for office on 4 July 1989 in the Tequendama Hotel in Bogotá. His popularity rating skyrocketed to 60%.

According to accounts the first assassination threats were calls made to Galán’s home telephone number after the Liberal Party convention to nominate an official candidate. Flyers were left in the mailbox threatening to kill or kidnap his children. An attempt to kill Galán with an RPG was thwarted while visiting Medellín on 4 August 1989. The assassination attempt was prevented by men working for Waldemar Franklin Quintero, the commander of the Colombian National Police in Antioquia. Accompanying Quintero and Galán was the mayor of Medellín, Pedro Pablo Paláez; both Paláez and Quintero would be killed within a few weeks of the assassination attempt. After these assassinations, Galán and his family restricted their travels, especially at night.

Later on, Galán’s staff received information from the Colombian intelligence services advising him of the presence in Bogotá of a group of hitmen with the intention to kill him. His staff advised him not to travel to the town of Soacha and that the trip to Valledupar was more suitable since he was also scheduled to attend a football match in nearby Barranquilla for a 1990 FIFA World Cup qualification match in which the Colombian team was going to play. At the last moment, Galán changed his mind and ordered his staff to prepare to go to Soacha. On August 18, 1989, Galán, who was being protected by eighteen armed bodyguards, was killed as he walked onto the stage to give a speech in front of 10,000 people in Soacha. At least ten others were wounded in the gunfire. This created a war that both sides were not wanting, one side being the Colombian Government and the other The Extraditables. Both sides saw deaths at a record toll.

César Gaviria, who had been Galán’s debate chief (“Jefe de Debate”) during the campaign, was proclaimed as his successor by Galán’s family and his supporters inside the Liberal party. He was elected president in 1990.

In 2004, new information in a letter written by one of the hitmen who had infiltrated his escort suggested that Galán’s assassination was executed with help of corrupt Colombian policemen and some of his own bodyguards, who had been bought off by the drug cartels, including Pablo Escobar and other drug lords. Most of the arrested presumed hitmen were killed in jail or shortly after their release, allegedly to silence them.

On 13 May 2005, a former Justice minister (1974) and congressman of the Colombian Liberal Party, Alberto Santofimio, known for his open connections to Pablo Escobar during the 1980s (Escobar joined Santofimio’s political movement), was arrested and accused of being the intellectual author of Galán’s murder.

On 11 October 2007, Alberto Santofimio was convicted to 24 years in prison. He was later released on appeal, but in August 2011 the Supreme Court reinstated the conviction and he surrendered himself.

On 25 November 2010 Colombian prosecutors issued an arrest warrant for the ex-director of the Colombian security agency (DAS), Retired Gen. Miguel Maza Márquez, for involvement in Galán’s murder. The prosecutors claimed that Maza intentionally lightened Galán’s bodyguard contingent to enable 18 August 1989 assassination. The Supreme Court convicted Maza in 2016 and sentenced him to 30 years in prison.