The basilica is the shrine tomb of the church's namesake, Saint Lawrence, one of the first seven deacons of Rome martyred in 258. Pope Pius IX, awaiting canonization into sainthood, is also buried at the basilica.
Before the present-day basilica was constructed, the estate upon which it sits was once home to a small oratory built by Emperor Constantine I. The emperor built it over the site on which it was believed that Saint Lawrence was executed. In the 580s, Pope Pelagius II commissioned the construction of a church over the site, in honor of the martyr. In the 13th century, Pope Honorius III commissioned the construction of another church in front of the older structure. It was adorned with frescoes depicting the lives of Saint Lawrence, and the first martyred deacon Saint Stephen, who is interred with Lawrence in the confessio under the high altar. The two structures were united as part of a program of urban renewal. Excavations have revealed several other crypts of various people, buried below street level. Saint Hilarius is buried here.
The portico, c. 1220, has Cosmatesque decoration by the Vassaletti family of craftsmen. The 13th century frescoes, which have been recently reconstructed, depict scenes from the lives of St Stephen and St Lawrence, both deacons and martyrs.
There are two ancient sarcophagi in the portico. Of special interest is a Christian one, possibly decorated in the 7th century on an older sarcophagus, with a relief depicting putti picking grapes. While vines and grapes are symbols of the Eucharist, this is not likely here. Two Romanesque stone lions were moved here from the old entrance.
The campanile was built in the 12th century. Just inside the entrance is the tomb of Guglielmo Cardinal Fieschi, died 1256, but entombed in an ancient sarcophagus, incidentally decorated with a relief depicting a pagan marriage feast.
The choir enclosure and pulpit has Cosmatesque decoration, and there is also a fine Cosmatesque Paschal candlestick made in the 12th or 13th century.
The antique Ionic capital on the column directly behind the pulpit has carvings of a frog and a lizard. On the triumphal arch are Byzantine mosaics from the 6th century, depicting Christ with saints. The confessio is below the high altar, and can be entered from the nave. Here, St Lawrence and St Stephen are enshrined. The latter was brought here from Constantinople by Pope Pelagius II when he restored the church. Behind the high altar is a papal altar with an inscription naming the makers, of the Cosmati family, and dating it to 1148.