In Lebanon, it was reorganized in 1963 as its central banking functions became the country's central bank, the Banque du Liban, and its commercial activity was continued as the Beirut-incorporated Société Nouvelle de la Banque de Syrie et du Liban (SNBSL).

[2] The branch was initially located inside Khan Antoun Bey [ar] in the Beirut Souks; in 1892 it moved to a new building on place des canons, now Martyrs' Square; and in 1906 to another new building in Western architectural style on the waterfront at the northern end of the street later named Allenby Street, while the previous location was repurposed as the Khedivial Hotel.

The BIO, by then controlled by the Banque de Paris et des Pays-Bas (BPPB), transferred to the new entity its existing branches in Aleppo, Alexandretta, Beirut, Damascus, Hama, Homs, Sidon, Tripoli and Zahlé, a transaction that was only completed in late 1921.

The formalization in 1923 of France's Mandate for Syria and Lebanon led to the bank's first name change to Banque de Syrie et du Grand-Liban, on 5 March 1924.

It kept operating during World War II despite the breakdown of communication between occupied France and its Levantine mandate territories following the Syria–Lebanon campaign of June–July 1941.

[9] In Lebanon, the country's central bank, the Banque du Liban, was formed in 1963 from the issuance-linked operations of the BSL.

[11] In the process of separation, the SNBSL secured ownership of the recently constructed BSL head office building on rue Riad El-Solh in downtown Beirut, with financing from the BPPB-controlled Ottoman Bank.