The cathedral was built by Archbishop John J. Glennon, a native of Ireland, who had a 42-year tenure as Archbishop of St. Louis. While many architects worked on the project over the years, the original design project was led by Barnett, Haynes & Barnett. This firm traces its origin to the Englishman George I. Barnett, who was called "the Dean" of St. Louis architecture for his contributions to the building of the city and for his influence on other architects.
His sons worked on the cathedral project. Thomas P. Barnett was a nationally recognized architect and painter who trained at the St. Louis School of Fine Arts. He had high regard for the classic period and was a proponent of classicism as a dominant architectural influence on the cathedral. Also, his brother George D. Barnett helped design the cathedral structure including the main altar, the baldachin, and other important decorations.
The cathedral is is known for its massive mosaic installation, which is the largest in the Americas. Actually, it is one of the largest in the world. The mosaic project was so intense that it was not completed until decades later in 1988. For this reason many different artists contributed over the decades. In 1912, installation of the mosaics began. Incredibly, the cathedral contains an estimated 41.5 million glass tesserae pieces in more than 7,000 different shades of color. They cover some 83,000 square feet.
The mosaics in the sanctuary walls and side chapels were designed and installed by Tiffany glass studios of New York. Mosaics in the rest of the church were done by a dozen artists. Some of them are mentioned here. The main body of mosaics were by Professor Otto Oetken, who labored in the cathedral for over 40 years. Some of the other artists included Hildreth Meiere, a female Art Deco artist from New York who worked on he mosaics in the 1940s and 1950s. Ravenna Mosaic company was also hired along with Emil Frei, Inc.
The father and son team Paul and Arno Heuduck worked on their mosaics for many years. The arch of the Last Judgment was completed in 1962 and the main dome in 1965 by Jan Henryk de Rosen of Poland, who depicted Biblical scenes from both the Old and New Testaments. The mosaics in the narthex depict the life of St. Louis, King of France, namesake and patron saint of the church. Mosaic artist Mary Reardon completed the mosaics in the 1980s.
A book could be written on the mosaics and their installation. Initially the German firm of August Wagner was contracted to install the mosaics. They set up shop in St. Louis, becoming the Ravenna Mosaic Company. Following the design of the artisans, mosaic artist Paul Heuduck undertook the red and gold designs of the transept galleries. He then completed the Arch of Triumph and the Arch of Creation, followed by the pendentives underscoring the main dome depicting the Doctors of the Church.
In 1930, the mosaics depicting the life of Saint Louis were completed in the Cathedral’s narthex, visually preparing the visitor for the growing grandeur inside. Shortly after World War II, a sacristy was added to the north end of the structure. Work on the mosaics continued. It was not to be completed until 1988, when the final two areas – the east and west transepts – were completed.
In 1997, the cathedral was designated as a Cathedral Basilica by Pope John Paul II, who honored the community with a visit on his historic last apostolic voyage to the United States in January of 1999. The symbols of the basilica status – the tintinnabulum (processional bell) and the ombrellino (processional umbrella) – flank the high altar reminding all of the special designation and awaiting the visit of the next pope.
In 2007 the great Cardinal Archbishop of St. Louis, Raymond Leo Burke, conceived a new shrine build in the cathedral's west transept to honor and foster devotion to the Sacred Heart of Jesus. The architect chosen was the esteemed and artistically illustrious Duncan Stroik, who enshrined a precious mosaic image of the Sacred Heart, produced by the Fabbrica di San Pietro Vatican Mosaic Studios. The mosaic image, measuring 3' x 4', is based on an original oil painting owned by the Archdiocese, presumably by a Spanish nineteenth century artist. The design of the shrine with the mosaic icon is free standing with a large pediment to frame the scene, lending verticality and prominence within the colonnaded apse. The Christian faithful gather here every day to pray and give honor Our Blessed Lord.