Salt returned to Ethiopia in 1809 on a government mission to explore trade and diplomatic links with the Tigrayan warlord Ras Wolde Selassie. On his return he published A voyage to Abyssinia, and travels into the interior of that country, executed under the orders of the British government in the years 1809 & 1810, and a collection of drawings entitled Twenty-four Views Taken in St Helena, The Cape, India, Ceylon, Abyssinia and Egypt. He later returned and continued a friendship with the Ethiopian warlord Sabagadis.
In 1815 Salt was appointed British consul-general in Cairo. During his time in Egypt he accumulated a collection of Egyptian artefacts, notably the head of Ramesses II from the Ramesseum, which he presented to the British Museum, and the sarcophagus box of Ramesses III which was bought by the Louvre in Paris. He also sponsored the excavations of Thebes and Abu Simbel, carrying out significant archaeological research himself at the pyramids of Giza and the Sphinx, and earned praise for his ability to decipher hieroglyphs from Jean-François Champollion.
He devoted himself to the task of assemble a collection of antiquities, although he was hindered in every possible way by Bernardino Drovetti, who, having been dismissed from his official post, now had the time personally to supervise the search of antiquities around the country. Drovetti had great advantages over his British rival because of his thorough knowledge of Egypt, where he had been living for many years by this time, and also thanks to his close friendship with the Pasha, Muhammad Ali of Egypt. But Salt was not easily discouraged and resorting to the same methods as his rival, he surrounded himself with agents who would not stop for nothing. The year he arrived in Cairo he had the good fortune to meet both Giovanni Battista Belzoni, an extraordinary individual who immediately became his main agent, and Giovanni D’Athanasi, a Greek known as Yanni, who worked for him in the Thebes area from 1817 to 1827. Thanks to his assistants, Salt was able to build up his important collection in just two years. This was sold to the British Museum for the sum of two thousand pounds, and was then followed by another, more important, collection, accumulated between 1819 and 1824, comprising no fewer than 4,014 objects. After being rejected by the British Museum because it was considered too expensive, this second collection was sold to Charles X of France for ten thousand pounds, and helped to enlarge the impressive collections of the Louvre.
Salt also managed to assemble a third collection, containing 1,083 objects. It was sold by auction, largely to the British Museum, in 1835, eight years after his death near Alexandria in 1827.