He was born Leandro Valencia Locsin on August 15, 1928, in Silay, Negros Occidental, a grandson of the first governor of the province. He later studied at the De La Salle Brothers in 1935 before returning to Negros due to the Second World War. He returned to Manila to study Pre-Law before shifting to pursue a Bachelor's Degree in Music at the University of Santo Tomas. Although he was a talented pianist, he later shifted again to Architecture, just a year before graduating. He married Cecilia Yulo, and one of their two children is also an architect.
The Tanghalang Pambansa of the Cultural Center of the Philippines, one of Locsin's most recognizable works.
An art lover, he frequented the Philippine Art Gallery, where he met the curator, Fernando Zóbel de Ayala y Montojo. The latter recommended Locsin to the Ossorio family that was planning to build a chapel in Negros. When Frederic Ossorio left for the United States, the plans for the chapel were canceled.
However, in 1955, Fr. John Delaney, S.J., then Catholic Chaplain at the University of the Philippines - Diliman, commissioned Locsin to design a chapel that is open and can easily accommodate 1,000 people. The Church of the Holy Sacrifice is the first round chapel in the Philippines to have an altar in the middle, and the first to have a thin shell concrete dome. The floor of the church was designed by Arturo Luz, the stations of the cross by Vicente Manansala and Ang Kiukok, and the cross by Napoleon Abueva, all of whom are now National Artists. Alfredo L. Juinio served as the building's structural engineer. Today, the church is recognized as a National Historical Landmark and a Cultural Treasure by the National Historical Institute and the National Museum, respectively.
On his visit to the United States, he met some of his influences, Paul Rudolph and Eero Saarinen. It was then he realized to use concrete, which was relatively cheap in the Philippines and easy to form, for his buildings. In 1969, he completed what was to be his most recognizable work, the Theater of Performing Arts (Now the Tanghalang Pambansa) of the Cultural Center of the Philippines. The marblefaçade of the building is cantilevered 12 meters from the terrace by huge arching columns at the sides of the building, giving it the impression of being afloat. A large lagoon in front of the theatre mirrors the building during daytime, while fountains are illuminated by underwater lights at nighttime. The building houses four theaters, a museum of ethnographic art and other temporary exhibits, galleries, and a library on Philippine art and culture.
In 1974, Locsin designed the Folk Arts Theater, which is one of the largest single-span buildings in the Philippines with a span of 60 meters. It was completed in only seventy-seven days, in time for the Miss Universe Pageant. Locsin was also commissioned to build the Philippine International Convention Center, the country's premiere international conference building and now the seat of the Vice Presidency.
He was also commissioned in 1974 to design the Ayala Museum to house the Ayala art collection. It was known for the juxtaposition of huge blocks to facilitate the interior of the exhibition. Locsin was a close friend of the Ayalas. Before taking the board examination, he took his apprenticeship at Ayala and Company (Now the Ayala Corporation) and was even asked to design the first building in Ayala Avenue, and several of their residences. When the collection of the Ayala Museum was moved to its current location, the original was demolished with Locsin's permission. The current building was dedicated in 2004, and was designed by the L. V. Locsin and Partners, led by Leandro Y. Locsin, Jr.
Locsin also designed some of the buildings at the UP Los Baños campus (UPLB). The Dioscoro Umali Hall, the main auditorium, is clearly an example of his distinct architecture, with its large canopy that makes it resemble the main theatre of the Cultural Center of the Philippines (CCP). Most of his work is concentrated on the Freedom Park, with the Student Union Building which was once damaged by a fire, the Carillon, the Continuing Education Center and the auditorium. He also designed the SEARCA Residences, and several structures at the National Arts Center (housing the Philippine High School for the Arts) at Mt. Makiling, Los Baños, Laguna.