In 1858, like William Morris, Philip Webb and Norman Shaw before him, Sedding became a pupil of the Gothic Revival architect, George Edmund Street (1824–1881).

The reredos, high altar, candlesticks, church plate, pulpit, lectern, choir stalls, encaustic tiles, statue of St Clement and rood screen were all designed by Sedding.

In 1875, he was elected a fellow of the Royal Institute of British Architects and moved from Bristol to set up in practice in London the following year, taking offices on the upper floors of 447 Oxford Street, next door to the premises of Morris & Co.

In 1876 Sedding met Ruskin under whose influence he developed a freer Gothic style, introducing natural ornament into his designs.

He placed an emphasis on texture and ornament; the naturalistic treatment of flowers, leaves and animals, always drawn from life; and the close involvement of the architect in the simple processes of building and in the supervision of a team of craftsmen employed direct.

[2] Sedding's buildings include the London churches of St Augustine of Canterbury, Highgate, London N6 (1884, completed by others),[3] Our Most Holy Redeemer, Clerkenwell (1887; in Italianate style), St Peter's Church, Ealing (1889) and Holy Trinity Sloane Street (begun in 1888 and completed by his pupil Henry Wilson),[4] which Sir John Betjeman described as "the cathedral of the Arts and Crafts Movement", although much of the decoration Sedding intended was not carried out.

With Henry Wilson (who completed the work on Sedding's death), he was commissioned by 6th Duke of Portland to create an extension to Welbeck Abbey to link the old building with the Riding School.