Trinity Congregational Church, later known as Union Chapel, is a former place of worship for Congregationalists and Independent Christians in Arundel, an ancient town in the Arun district of West Sussex, England.

Protestant Nonconformism—Christian worship which stood apart from both the Established Anglican Church and Roman Catholicism—was successful and influential in Sussex from the 17th century.

[2] A period of decline for Nonconformist worship was reversed in the late 18th century, and a group of Independent Christians (who advocated Congregationalist polity) began meeting in 1780.

[2] George MacDonald, the Scottish poet and children's writer, became the pastor in 1850, but his views and sermons were unpopular and he resigned three years later.

[2] He had trained as a Congregational pastor at Highbury Theological College, but did not finish the course which he began in 1848 and took up the position at Arundel after spending some time as a travelling preacher.

His preaching was influenced by his poetry and did not suit the congregation's beliefs; he left in May 1853 after his stipend was cut, and turned to writing.

Robert Abraham's design represents a "brief appearance" of the Romanesque Revival style in the architectural history of Nonconformist chapels in Sussex.

[2] Ian Nairn dismissed the building as "not good",[12] and notes its similarity to the "gloomy" town hall and council offices of 1836 by Abrahams.

[4] The first floor has three tall windows with round heads,[5] and the centrally placed entrance at ground-floor level is set into a similar arch flanked by capital-topped colonnettes[4] (small medieval-style shafts).

[4] Inside, the original gallery on the north wall (surrounding the entrance) survives, but those on the west and east sides have been removed.