[7][8] The current site of the General Post Office is also situated over the now entirely enclosed Tank Stream, which was once the primary source of fresh water for the Penal Colony of New South Wales, shortly after the arrival the First Fleet on 26 January 1788, under the direction of Arthur Philip, the First Governor.

The central axis of its primary façade is also aligned with the ANZAC Cenotaph, a memorial located at the centre of Martin Place, dedicated to the soldiers who fought in World War I.

[9] Through the articulation of the northern façade, with a well maintained continuity in proportion between the three types of openings along the levels of the GPO generated a harmonious module which allowed the full sense of grandeur to be realised.

"[4] Barnet's deliberate insertion of an arcade, proportional intents and the centring of the campanile along what was once a lane way were all architectural moves designed to develop a space which would link Pitt and George Streets.

[10] The existence of Martin Place is largely "owed to the construction of the General Post Office"; Barnet knew changes would be made "because the completed building would clearly lack what was appropriate to it, a dignified square.

[4][13] Writing about the newly modified post office in 1848, Joseph Fowles commented that it was "one of the most important buildings in the colony, not merely as regards to the structure, but as being the centre and focus, the heart, as it may be termed, from which the pulse of the civilisation throbs to the remotest extremity of the land.

[13][14] It was at this time that James Barnet, having recently been appointed the first Colonial Architect of New South Wales, was instructed to prepare plans for a new post office on the George Street segment of the present site.

[16] Eventually however, the former GPO was demolished and today, one of its six Doric columns still stands in Mount Street Plaza, North Sydney, whilst another can be found off Bradleys Head, Mosman.

Russell and Co."[16][19] Early progress proved to be a slow and difficult process, particularly due to the need to enclose the Tank Stream running below the foundations and to ensure construction would not affect adjoining buildings.

[16][13] A prominent newspaper of the time reported that the "ponderous keystone" was quarried at Pyrmont and weighted 26 tons (26.5 metric tonnes), highlighting that it was one of many such stones used in the construction of the building and described as being "without parallel in the city.

Shortly after the official keystone setting ceremony, on 8 September 1869, news reports began anticipating how "the building will be one of the finest specimens of architecture in the colony—a credit to the city, and a monument to the ability of the colonial Architect by whom it was designed.

"[22] It was also at this time that suggestions for the widening of the adjacent St. Martin's Lane began, with a newspaper commenting on 20 January 1870 that "a decent thoroughfare...would add to the architectural reputation of the city; but, without such an approach, it will probably furnish a subject for the laughter and contempt of strangers who may visit us.

Designed to provide additional space and extend the impressive arcade further east to Pitt Street, it has since been historically noted that Barnet had conceived of this extension in as early as 1868, when stage one of the GPO was first being considered.

[1] Although the construction of the Pitt Street extension was completed successfully and the building topped out by 1887, a final issue, concerning the clock tower (which Barnet referred to as a campanile) arose as a new source of disagreement.

"[24] Barnet was however unable to attend the stone laying ceremony for this completion, as he had travelled to Europe to make important notes on art and architecture, continuing research and observations to justify the designs of the Pitt Street carvings.

It was refurbished through the work of Sydney-based architectural practice Clive Lucas Stapleton & Partners and subsequently the building houses shops, restaurants, hotel rooms, and the foyer of two adjoining tower blocks.

[38] In 2019, Stonemason and Artist, an expert team with a combined stonemasonry experience of 334 years, undertook a 38,000-hour laborious, chemical-free cleaning process to restore the building’s façade to its former glory.

"[13][40] The official opening ceremony speech was made by the General Post Office the Postmaster-General, (Sir) Saul Samuel who paid a glowing tribute to the work of Barnet.

[20] Barnet, who was himself also present at the opening ceremony gave a speech in which he hoped that the GPO would be "taken as a sure sign of the permanent advancement of the colony and its vastly increased importance and prosperity..." and further celebrated a doubling in postage handling capacity, noting specifically in his statement to the press that the new building had a floor space of 35,247 square feet.

[4] Throughout its twenty five year construction process, the GPO was marred by two major controversies, the first of which related to the selection of bells for the campanile clock and the second, more significantly, to the commission of Italian immigrant sculptor Tommaso Sani's "realistic" depictions of people for the carvings along the Pitt Street arcade.

[43] The new electric telegraph technology connected Australia with the world in a matter of days ending the tyranny of distance which, since colonial times, had burdened commerce and trade relations.

In reality the Sani reliefs were late less sophisticated examples of the 1840s Italian realist style known as Verismo whose leading exponent was Vicenzo Vela (1820–1891), but drew the ire and derision of an uniformed elite one of whose members was, Frederick Darley (later, the Chief Justice of NSW) who "denigrated the carvings as caricatures", and such was the controversy surrounding these works that it led to debates on aesthetics and taste within the New South Wales Legislative Assembly between 1883 and 1890 in which Barnet was himself called upon to justify and defend his decision.

The severity of the carvings as a matter of aesthetic taste was taken so seriously that it was raised by the then vice-president of the Executive Council of the third Parkes Ministry in the New South Wales Legislative Assembly, Sir Frederick Darley (later, sixth Chief Justice of NSW), who was shocked by what he saw and tabled questions in parliament on 12 April 1883.

In a scathing review, formed from descriptions and photographs sent to him, he concluded that the carvings could be viewed with "nothing short of consternation and...disgust...a shameful disfigurement...ugly and degrading to the sense of sight.

"[16] Despite this setback, Barnet continued to reject these reports and criticisms, arguing that the photographs for study, taken on a level elevation rather than from Pitt Street, failed to correctly represent the final perspective and that the building scaffolding hindered key views to the carvings.

[40] The sandstone which was carved from Pyrmont to form the mezzanine galleries and spandrels of the arcade were done in sizes which had never been attempted in Australia and the internal domed vaults demonstrated Barnet's innovative use of fireproof concrete.

Historians have since noted that Barnet's design was an "eminently practical solution" which not only increased pedestrian access and a transition between exterior and interior of the building, but also gave the façade a sense of depth and character.

[20][12] When the GPO was first opened to the public 1874, Barnet confirmed, in a statement to the press that "The style chosen for the design is Italian Renaissance, and was necessarily adapted to the uses of the building and the nature of the site.

[1] The three major street-facing facades all consist of a tripartite articulation and is composed from load bearing Sydney sandstone, supported by the granite columns which form the Martin Place arcade.

[61] Criticism of the sale described it as simply "asset stripping" and referred to the government's lack of care of the city's heritage and its past, as well as doubts over the new owners' ability to protect the building in the future.