From A Dictionary of Irish Artists 1913
Was born in Dublin, a brother of the foregoing. Going to London he found employment as an assistant to Nollekens and did the carving of many important works which came from that artist's studio. The statue of WilliamPitt in the Senate House at Cambridge, done in 1809, for which Nollekens was paid three thousand guineas, was carved by Gahagan, who was paid but a small sum for his work. Nollekens left him by his will £100. In 1809 he received a premium of fifty pounds from the British Institution for "Sampson breaking his Bonds." He was a frequent exhibitor in the Royal Academy from 1802 to 1835, chiefly of monumental designs with occasional portrait statues and busts. In Westminster Abbey is a bust of Dr. Charles Burney by him, and in St. Paul's Cathedral a monument to Sir Thomas Picton. The bronze statue of the "Duke of Kent" in Park Crescent, Portland Place, and the figures of Isis and Osiris in front of the Egyptian Hall, Piccadilly, are his work. A bust of " William Pitt " by him was mezzotinted by E. Bell, and one of "Lord Nelson" by W. Barnard in 1805. In the "European Magazine," 1823, is an engraving by J. Thomson of a marble bust of Charles Hutton, then belonging to the Philosophical Society of Newcastle-on-Tyne.
There were several other members of his family, all sculptors and modellers, viz.: EDWIN GAHAGAN, his brother, who was an assistant to Richard Westmacott, R.A., and was killed by the fall of the statue of Canning, now in Parliament Square, upon which he was working. GEORGE GAHAGN, who worked for Nollekens and was left a legacy by him of twenty pounds; L. GAHAGAN, V. GAHAGAN, C. GAHAGAN and SALLY GAHAGAN; some, at least, of whom were sons of either Laurence or Sebastian.