In October 1877 Blackmann moved to Sydney, where he was engaged by James Barnet, the New South Wales Colonial Architect and prepared detailed drawings of Callan Park and the Garden Palace for the Sydney International Exhibition of 1879.
He was the supervising architect for the Exhibition Refreshment Pavilion and for the Goulburn Government Offices.

In June 1880, Blackmann formed an architectural partnership with Varney Parkes, who was a 21-year-old cadet in the Colonial Architect's Office and son of the Premier Sir Henry Parkes.
 The partnership flourished for over five years until dissolved in September 1885, when Varney Parkes was elected to the New South Wales Parliament.
The 1883 design of the Victorian Free Classical style Erskinville Public School is jointly attributed to Blackmann and Parkes.

Also in 1880, Blackmann designed his home Oybin, part of the Johnston Street Group built by John Young in the Sydney suburb of Annandale.
This group originally consisted of eight houses, of which six are still standing.
Blackmann lived in Oybin until 1885.
It was divided into six flats in 1927 and gutted by a "suspicious" fire in 1976.
It was subsequently restored during the 1990s and renovated further in 2007.
It is now listed on the local government heritage database.

After dissolution of the partnership on 4 September 1885, Blackmann maintained as clients the Australian Joint Stock Bank, Mercantile Bank of Sydney and the Australian Mutual Provident Society.
 During the year as a sole practitioner he advertised tenders for three residences, six banks, five commercial buildings, additional public buildings for Randwick Council as well as minor works.

Negotiations to form another partnership with John Sulman concluded October, 1886  and the first tender was advertised on later that month.
 It would appear that Blackmann, then aged 51 suffered a ‘mid life crisis’ and sailed for New Zealand from Melbourne on SS Waihora on 2 December 1886.
In October 1877 Blackmann moved to Sydney, where he was engaged by James Barnet, the New South Wales Colonial Architect and prepared detailed drawings of Callan Park and the Garden Palace for the Sydney International Exhibition of 1879. He was the supervising architect for the Exhibition Refreshment Pavilion and for the Goulburn Government Offices.
In June 1880, Blackmann formed an architectural partnership with Varney Parkes, who was a 21-year-old cadet in the Colonial Architect's Office and son of the Premier Sir Henry Parkes.  The partnership flourished for over five years until dissolved in September 1885, when Varney Parkes was elected to the New South Wales Parliament. The 1883 design of the Victorian Free Classical style Erskinville Public School is jointly attributed to Blackmann and Parkes.
Also in 1880, Blackmann designed his home Oybin, part of the Johnston Street Group built by John Young in the Sydney suburb of Annandale. This group originally consisted of eight houses, of which six are still standing. Blackmann lived in Oybin until 1885. It was divided into six flats in 1927 and gutted by a "suspicious" fire in 1976. It was subsequently restored during the 1990s and renovated further in 2007. It is now listed on the local government heritage database.
After dissolution of the partnership on 4 September 1885, Blackmann maintained as clients the Australian Joint Stock Bank, Mercantile Bank of Sydney and the Australian Mutual Provident Society.  During the year as a sole practitioner he advertised tenders for three residences, six banks, five commercial buildings, additional public buildings for Randwick Council as well as minor works.
Negotiations to form another partnership with John Sulman concluded October, 1886  and the first tender was advertised on later that month.  It would appear that Blackmann, then aged 51 suffered a ‘mid life crisis’ and sailed for New Zealand from Melbourne on SS Waihora on 2 December 1886.
C. H. E. Blackmann