St Peter's opened amid great celebration on 16^th April 1863, at that time the only church in Britain in the Roman Basilican style. The Irish architect John Miller Bryson worked from plans drawn by Francesco Gualandi of Bologna, which in turn were modelled on the Basilica of San Crisogono in Trastevere, Rome. St Peter's was originally the 'Church Of All Nations' and throughout the 1860s attracted congregations of many nationalities. A Polish chapel was established in the crypt. The excellence of the music attracted people of many faiths.

The choir was outstanding and regular concerts were held, featuring distinguished soloists and orchestras. The Italian Church, as it soon became known, established itself with great success. The choir loggia and organ were built in 1886. The magnificent organ which can be seen today is part of the original by the Belgian craftsman Anneesen and it was regarded as the finest in the country at the time of its installation. It was restored in 1959 using many of the original features, and again in 1995. Maintaining the tradition of fine singing at St. Peter's, it has accompanied may exceptional singers, including the great tenor, Beniamino Gigli. Looking up from the central nave, the ceiling is dominated by a fresco depicting St. Peter in triumph, carrying symbols of his authority and martyrdom (Gauthier of Saluzzo 1896)    Enough money was found to complete the presbytery in 1865-66. The campanile and new loggia on Clerkenwell Road were designed by Francis Tasker and completed in 1891.

The façade of the church consists of a loggia and a portico with two arches, above which are three alcoves. The central alcove contains a statue of Christ, whilst the side alcoves contain statues of St. Bede and St. George. Between the alcoves are two large mosaics depicting the miracle of the fishes and Jesus giving the keys of the Kingdom of Heaven to St. Peter. Above the façade is a 33-metre-high bell tower, built in 1891 which houses a huge bell known as "The Steel Monster". In the loggia are two important plaques, one to veterans of the First World War and the other to 446 Italians who lost their lives on the Arandora Star.