He was educated in Bogotá and England.
He worked in the family firm, representing it in New York. Eventually, he founded a commercial bank. Although he had early been involved in politics, he did not achieve national importance until the Liberal Party convention in 1929. The long-ruling Conservative Party was divided, and López issued a call to Liberals to take power with new ideas and programs. The old- line Liberals prevailed at the convention, but the party did succeed in electing Enrique Olaya Herrera president in 1930, in coalition with dissident Conservatives.
López served under Olaya as ambassador to the United Kingdom. However, he became the center of a group of young, progressive-minded Liberals. Named the party’s presidential candidate for 1934, he was elected when the Conservative Party, led by Laureano Gómez, abstained from the election.
Although limited in both scope and effectiveness, the “Revolution on the March” made López the most popular president in modern Colombian history. However, Olaya’s followers, including big businessmen, saw the reforms, especially those concerning labor and state economic policy, as potentially dangerous to their interests. The Conservatives railed against what they called anticlericalism and the general direction of the López administration. Faced with mounting opposition in Congress and from the traditional political leadership, he slowed his program considerably in 1937.
The following administration of Liberal Eduardo Santos (1938-1942) was called “the pause.” No significantly new social programs were begun, and the Liberals were divided. López won a second term in 1942.
López was briefly arrested by a rebellious army unit in 1944. Although the coup failed, it further discredited him. López finally resigned and turned the presidency over to Alberto Lleras Camargo in 1945.
Although López represented Colombia in the United Nations between 1946 and 1948, he played no prominent role in national politics until the 1950s. Then, as Colombia was engulfed by widespread rural violence and military dictatorship, he originated the idea of a National Front government of Liberals and Conservatives which was eventually adopted.