On 19 October 1356, his grandmother Joan de Geneville, 2nd Baroness Geneville, widow of the first earl, died, and Roger inherited her vast estates, including Ludlow Castle, which was thereafter the Mortimer family seat and power base.
In the following years, he became a member of the Royal Council and was appointed Constable at the castles of Montgomery, Bridgnorth in Shropshire, and Corfe in Dorset.