By the end of the nineteenth century, the society had established a large non-resident membership in the overseas empire and within the United Kingdom among those not living in the London area. At first a network of honorary corresponding secretaries was formed to manage the society's affairs outside London. In 1910 it authorised the establishment of local branches to increase membership and extend the scope of its activities. The first UK branch was formed in Bristol in 1913 and the first overseas branch in Christchurch, New Zealand during the same year. Several began as local committees. The branches expanded in number and independence following the Second World War.

These archives document the branches' foundation, relations with the London headquarters and the wide range of social, cultural and educational initiatives they sponsored. Not all branches were successful or of long duration, and many did not regularly transmit accounts of their activities to headquarters, so individual branch records are often fragmentary. The society's journals 'United Empire' and 'Journal of the Royal Commonwealth Society' often printed reports of branch activities however.