Fahey was born at Paddington, then a village near London, and at first studied engraving under his uncle, John Swaine.
Afterwards he became a pupil of George Scharf, and then went to Paris, where he studied from life, making full-size drawings of dissections, which he reproduced on stone for the use of anatomical students.
His earliest exhibited work, a "Portrait of a young Gentleman", appeared at the Royal Academy in 1825, and was followed in 1827 by drawings of the church of St. Jacques at Dieppe and the cathedral of Notre-Dame at Paris.
His works, mostly landscape compositions, in which he introduced figures and groups, were seldom absent from its exhibitions, and his official services were long given without any remuneration.
In 1853, 1855, and 1857 he again sent landscape drawings to the Royal Academy, and in 1856 he was appointed drawing-master at the Merchant Taylors' School, from which post he retired with a pension after twenty-seven years' service.