Parts of the unfinished building and Gaudí's models and workshop were destroyed during the Spanish Civil War by Catalan anarchists. The design, as now being constructed, is based both on reconstructed versions of the lost plans and on modern adaptations. Since 1940 the architects F. Quintana, I. Puig Boada, Ll. Bonet i Gari and F. Cardoner have carried on the work. The current director and son of Ll. Bonet, J. Bonet i Armengol, has been introducing computers into the design and construction process since the 1980s. Sculptures by J. Busquets, E. Sotoo, and the controversial J. Subirachs decorate the fantastical façades.

Every part of the design of La Sagrada Família is rich with Christian symbolism, as Gaudí intended the church to be the "last great sanctuary of Christendom". Its most striking aspect is its spindle-shaped towers. A total of 18 tall towers are called for, representing in ascending order of height the twelve Apostles, the four Evangelists, the Virgin Mary, and, tallest of all, Jesus Christ. The Evangelists' towers will be surmounted by sculptures of their traditional symbols: a bull (St Luke), an angel (St Matthew), an eagle (St John), and a lion (St Mark). The central tower of Jesus Christ is to be surmounted by a giant cross; the tower's total height (170 m) will be one metre less than that of Montjuïc, as Gaudí believed that his work should not surpass that of God. Lower towers are surmounted by communion hosts with sheaves of wheat and chalices with bunches of grapes, representing the Eucharist.

The church will have three grand façades: the Nativity (eastern) façade, the Glory façade (yet to be completed), and the Passion (western) façade. The Nativity facade was built before work was interrupted in 1935 and bears the most direct Gaudí influence. The Passion façade is especially striking for its spare, gaunt, tormented characters, including emaciated figures of Christ being flogged and on the crucifix. These controversial designs are the work of J. Subirachs. The towers on the Nativity facade are crowned with geometrically shaped tops that were probably influenced by Cubism (they were finished around 1930). The intricate decoration is loosely related to the style of Art Nouveau but reflects Gaudí's unique ideas.

Themes throughout the decoration include words from the liturgy. The towers are decorated with words such as "Hosanna", "Excelsis", and "Sanctus"; the great doors of the Passion façade reproduce words from the Bible in various languages including Catalan; and the Glory façade is to be decorated with the words from the Apostles' Creed. Areas of the sanctuary will be designated to represent various concepts, such as saints, virtues, sins, and secular concepts such as regions of Spain, presumably with decoration to match.

The building works are expected to be completed around 2026, the 100th anniversary of Gaudi's death, although the likelihood of meeting this date is disputed. Computer modelling has been used for the detailed design of the intricate structure of supporting columns inside the basilica. CAD/CAM technology has been used to speed up the construction of the building; initially, the construction work was expected to last for several hundred years, based on building techniques available in the early 1900s. The construction work calls for many pieces of stone to be machined to unique shapes, each being subtly different from the next, and these pieces are now being machined accurately off-site, reducing the overall construction time.