Born in Richmond, Surrey, Hallswelle began his career working for the Illustrated London News. In 1854 he was sent to make drawings in Scotland, and having received other commissions there, he decided to stay. He settled in Edinburgh and studied at the Royal Scottish Academy, of which he was elected an Associate in 1866. Meanwhile in 1862 he had made his debut at the Royal Academy where he continued to exhibit for thirty years, although he was never a member. His early paintings were English or Scottish genre scenes and landscapes, but in 1868 he made the first of several visits to Italy, and from the following year until 1879 he showed almost nothing but Italian subjects, mostly Roman but occasionally Venetian, at the Academy. The present picture, which was begun in Edinburgh in 1869 but finished long after the artist had returned to London in 1871 (he lived in Old Bond Street until 1878, when he moved to Albemarle Street), was the last of these Italian subjects, and probably, considering the length of time it was in progress, the most ambitious.

Halswelle witnessed the scene in June 1869 and recorded it as follows in his diary:
Awaiting the appearance of the Pope on the balcony of the church, numbers of country people in their picturesque costume were grouped about the open space fronting the portico, dotting the scorched grass with masses of colour; a low wall, running at right angles with the church, had been early taken possession of by some of the contadini, their white pannos and gay dresses telling intensely in the brilliant sunshine against the deep blue sky beyond. The monastery and church of Santa Croce in Gerusaleme (and) part of the Claudian aqueduct in the middle distance, with the long line of the Campagna (as far as) the Alban and Sabine mountains, made up a scene of beauty to be long remembered.

St John Lateran was built by the Emperor Constantine in the fourth century as the cathedral church of the papacy; after many vicissitudes, it was restored by Borromini, and a new facade was added by Alessandro Galilei in 1736. S. Croce in Gerusaleme, a church associated with St Helena's discovery of the true Cross, stands some way to the east, and beyond there was indeed in Hallswelle's day a beautiful view over the Campagna to the Alban and Sabine hills; this, however, is now ruined by the spread of modern suburbs. The Pope whose blessing is being awaited was the famous Pio Nono (reigned 1846-1878), who began his pontificate as a liberal but was turned into an arch-reactionary by the revolution of 1848 and was responsible for the controversial doctrine of papal infallibility.

The picture evoked varied reactions when it appeared at the Royal Academy. The Times was not impressed by the work of this 'facile painter', maintaining that 'the vivid colouring of costumes and other palpably pituresque points of his models are forced to a point which defeats itself'. The Athenaeum was more enthusiastic, though it still had reservations. Describing the picture as 'large, effective, and pretentious', it continued: 'The conventionality of the sunlight proves the limits of the artist's fidelity to nature. Apart from this shortcoming, the illumination is brilliant and the effect strong. The designing of the figures is highly meritorious, from the variety and spontaneity of their actions, expressions, and characters. The picture is hung on high, but, being painted in a coarse and thin fashion, it does not suffer from that.' The warmest praise came from the Art Journal, which felt that this 'magnificent daylight picture' was 'one of the best works (the artist) has sent to the Academy for some time.'