[2][page needed] He was articled to Thomas Fulljames (1808–1874) in Gloucester and acted as clerk of works for the latter's Edwards College, South Cerney (Glos) in 1838–39.

From about 1885 onwards, when he seems to have semi-retired, St. Aubyn worked in partnership with Henry John Wadling (d 1918), who entered his office as a pupil in 1858 and remained as his assistant and managing clerk.

He practised chiefly in London and developed a practice which extended all over southern England, but he also kept an office in Devonport for part of his career, and he was employed particularly extensively in Devon and Cornwall.

Apart from this local connection, there are clusters of his work in Gloucestershire (no doubt deriving from his years in Fulljames' office), Kent, Reading, Cambridgeshire and Leicestershire.

His restorations often amounted to wholesale or partial rebuilding, and were seen by later generations as unnecessarily brutal; Sir John Betjeman was among St Aubyn's 20th-century detractors.

[10] Derbyshire: Duffield, 1846; St Andrew's Church, Cubley, 1872–74 Devon: Stoke Fleming, 1871; Dawlish, 1874; St. Giles-on-the-Heath, 1878 Gloucestershire: Daglingworth, 1845–51; Church of All Hallows, South Cerney, 1861–62; Standish, 1867; Owlpen, 1874–75; Dursley, 1888–89 Hampshire: Sherborne St John, 1854, 1866–84 Herefordshire: Cusop, date unknown Kent: Cliffe, 1864; Boughton-under-Blean, 1871; Lympne, 1878–80; Harbledown, 1880; Sheldwich, 1888 Leicestershire: Whitwick, 1848–50; Holy Trinity, Ashby-de-la-Zouch, 1866; Ashby Parva, 1866; Appleby Magna, 1870–72; St Helen, Ashby-de-la-Zouch, 1878–80 Lincolnshire: Theddlethorpe All Saints, 1885 Northamptonshire: Maidwell, 1891 Nottinghamshire: Eakring, 1880–81 Suffolk: Little Glemham, 1857–58; Woolverstone, 1888–89; Sternfield, date unknown Surrey: Addington, 1876