John Pollard Seddon FRIBA (19 September 1827 – 1 February 1906) was an English architect. His father was a cabinetmaker and his brother Thomas Seddon (1821–1856), a landscape painter. He was educated at Bedford School.
J. P. Seddon was a pupil of Thomas Leverton Donaldson, though Donaldson was a classical architect and Seddon preferred the Gothic Revivalism of John Ruskin.
Between 1852 and 1863 J. P. Seddon formed a partnership with John Prichard. Many of their major commissions were church restoration works, most famously for Llandaff Cathedral. In 1871 he submitted a design in a competition for Holloway Sanatorium.
C. F. A. Voysey was articled as a pupil of Seddon in 1873.
From 1884 to 1904 he was in partnership with John Coates Carter.
In 1904 he was Diocesan Architect for London and designed a gigantic Imperial Monumental Halls and 168 metre tower to be added to Westminster Abbey. It was supposed to restore the dominance of Westminster Abbey over the surrounding crowd of towers and monuments. However, the cost of construction was prohibitive and it remained unbuilt.
His works include the University College of Wales building in Aberystwyth, St Peter's Church, Ayot St Peter, Hertfordshire, St Catherine's Church, Hoarwithy, Herefordshire and, with John Prichard, the Church of St John, Llandenny, 1858-9 rebuild of St Mary's Church, Aberavon, and limited extensions to Dingestow Court, Monmouthshire, including the stables. He was also a prolific designer of furniture, metalwork, stained glass, tiles and ceramics.