Adopting a medical career, he became a pupil of Ralph Fletcher of Gloucester, (a surgeon of considerable eminence in his profession, and of some note as a collector of pictures), and later married his daughter.

At first he practised freely the removal of the tonsils as an aid to recovery from deafness, but in later life experience led him to modify his views, and he performed tonsillectomy much less often.

Yearsley was less scientific than either George Pilcher or Joseph Toynbee, and, though original in his views and bold in expressing his opinions, he too often spoilt his cause by his controversial temperament.

Jointly with two other members of his profession, Dr. Tyler Smith and Dr. Forbes Benignus Winslow, he founded the ‘'Medical Directory'’, becoming its sole proprietor on the retirement of his two partners.

A memorial plaque on his former clinic at 32 Sackville Street, Piccadilly was unveiled on 27 May 1994[2] which reads "Westminster City Council Dr. James Yearsley, MD, MRCS, LRCP, 1805 - 1869, founded the Metropolitan Ear Institute here in 1838.