As a young adult he moved to London, where he studied architecture under the Anglo-Catholic architect Richard Cromwell Carpenter, whose medieval Gothic style of design was to have a lifelong influence on Mountfort.
As a young adult he moved to London, where he was an early pupil of George Gilbert Scott (from 1841-46). He also studied architecture under the Anglo-Catholic architect Richard Cromwell Carpenter, whose medieval Gothic style of design was to have a lifelong influence on Mountfort.