[1] The Bethel Union's third church was designed by John Bibb, in the Victorian Free Classical style, built of well-executed sandstone ashlar, with a slate roof.

The building is of high architectural and historical importance, and the original church is a grand space and a rare and precious reminder of an expansive early Victorian preaching auditorium.

Around this time the Bethel Union was in financial difficulties, and eventually, in 1895, the Mariners' Church was leased to the Missions to Seamen, an organisation originating in England in 1835, and starting in Sydney with the work of John Shearston in 1872.

An extra storey was added with four columns to support the beam structure of the upper floor which consisted of a central chapel with compartments on either side.

Kent added rooms to the George Street facade which were in the Federation Free Classical style, converting the façade into a three-storey ensemble.

[1] In 1971 the Mariners' Church complex was resumed by the Sydney Cove Redevelopment Authority (SCRA) and the Bethel Union was relocated to Flying Angel House, 11-15 Macquarie Place, opened in 1977.

The site had previously been that of the boat builders house and garden, part of the Government Boatyard which also encompassed Cadmans Cottage to the south.

[1] The first John Bibb structure was built in Victorian Free Classical style in temple form, resulting in a single large prismatic volume with two projecting wings with a cruciform plan symmetrical about two axes.

An extra storey was added with four columns to support the beam structure of the upper floor which consisted of a central chapel with compartments on either side.

In 1927 a new chapel was built in the Inter-War Mediterranean or Romanesque style at ground level and a new balcony was erected on a base of retaining walls and piers of cement rendered load bearing brickwork facing Circular Quay West.

In 1931 a stone cottage erected 30 years before on the north-east corner of the site was demolished and a new dwelling for the Mission Chaplain was built, designed by N. W. McPherson, which became part of the Davidson Wing, and was not completed until after World War II.

2008 complete refurbishment[1] As at 30 March 2011, The Mariners' Church and site are of State heritage significance for their historical and scientific cultural values.

The existing Mariners' Church complex is an important streetscape element in a major historic precinct and its buildings display characteristics of the highest aesthetic calibre, including fine details and use of two applications of the Free Classical style - one early Victorian, the other Federation.

The fabric of the Mariners' Church evidences high quality workmanship and early use of steel technology and illustrates subsequent application of conservation values and principles.

The site is highly significant for its historical and occupational associations with The Rocks and the maritime nature of Sydney, including the early Dockyard and Robert Campbell's house and waterside warehouse.

The original building and the George Street façade and other exteriors are important examples of the work of the significant architects John Bibb (early to mid 19th century) and Harry C. Kent (Federation period) respectively.

The former Mariners' Church is a fine early example of the Victorian Free Classical style of architecture in the form, space and surviving detail of the first chapel.

The extensions completed in 1909 are a good and representative example of Federation Free Classical architecture, and are an ingenious solution to a difficult design problem.

[6] The building occupies a key location at the confluence of Hickson Road and George Street and has a landmark quality being at the crown of a slight rise, providing a focus for a variety of spatial vistas and even different levels of views.

The construction of the building is associated with the first application in Sydney of the principle of the eight-hour working day and thus with the early influence of the trade union movement.

The first Mariners' Church is a good example of traditional masonry construction, displaying fine workmanship and detailing, including different kinds of ashlar tooling as well as the use of shell-lime mortar.