Garran was a keen supporter of the federation movement, and became acquainted with leading federalists like George Reid and Edmund Barton.

His first duty was to write the inaugural edition of the Commonwealth Gazette, which contained Queen Victoria's proclamation authorising the creation of a federal government.

Over the following three decades, Garran provided legal advice to ten different prime ministers, from Barton to Joseph Lyons.

Hughes, who was simultaneously prime minister and attorney-general, appointed him to the new position of solicitor-general and delegated numerous powers and responsibilities to him.

Garran published at least eight books and many journal articles throughout his lifetime, covering such topics as constitutional law, the history of federalism in Australia, and German-language poetry.

"[5][6] He advocated free trade and Federation while editor of The Sydney Morning Herald and later promoted these ideas as a member of the New South Wales Legislative Council.

He was employed for a year with a firm of Sydney solicitors, and in 1890 served as associate to Justice William Charles Windeyer of the Supreme Court of New South Wales.

"[20] On joining the bar soon became involved with Edmund Barton Q.C., later the first Prime Minister of Australia, and the de facto leader of the federation movement in New South Wales.

Garran, along with others such as Atlee Hunt, worked essentially as secretaries to Barton's federation campaign, drafting correspondence and planning meetings.

"[22] In June 1893, when Barton's Australasian Federal League was formed at a meeting in the Sydney Town Hall, Garran joined immediately and was made a member of the executive committee.

[23][24] In 1897, Garran published The Coming Commonwealth,[25] an influential book on the history of the Federation movement and the debate over the 1891 draft of the Constitution of Australia.

On the evening before the convention's last day, Barton had gone to bed exhausted in the small hours, Garran and Charles Gavan Duffy finishing the final schedule of amendments at breakfast time.

[28] The convention concluded successfully, approving a final draft which ultimately, aside from a small amendment arranged at the last minute in London, became the Constitution of Australia.

[1] In Garran's opinion the approach, which was put into practice many years before the similarly principled plain English movement became popular in government in the 1970s, was intended "to set an example of clear, straightforward language, free from technical jargon.

[35] The style was also once parodied by foundation High Court Justice Richard O'Connor as follows: Every man shall wear – (a) Coat (b) Vest (c) Trousers Penalty: £100.

Initially the department contracted private law firms to actually conduct the litigation, but in 1903 the office of the Commonwealth Crown Solicitor was established, with Charles Powers the first to hold the job.

Billy Hughes, Attorney-General in the Fisher government at the time, later said Garran would have been appointed "but for the fact that he is too valuable a man for us to lose.

[49] The War Precautions Regulations had a broad scope, and were generally supported by the High Court, which adopted a much more flexible approach to the reach of the Commonwealth's defence power during wartime.

to which Garran replied that it was Haydn's melody to "Gott erhalte Franz den Kaiser", and as it was used as the tune to several hymns "it was probably sung in half a dozen churches in Sydney last Sunday."

[58] Garran viewed some similarities between British Prime Minister David Lloyd George and United States President Woodrow Wilson where others saw only differences, since Lloyd George "also had a strong vein of idealism in his character", and Wilson could be pragmatic when the situation called for it, such as in discussions relating to American interests.

[59] Garran also met other political and military leaders at the conference, including T. E. Lawrence, "an Oxford youth of 29 – he looks 18", who was modest and "without any affectation... in a company of two or three [he] could talk very interestingly, but at a larger gathering he was apt to be dumb.

[64][better source needed] In 1930, he was asked by the Scullin government to provide an opinion on whether Norman Lindsay's novel Redheap was indecent and obscene within the terms of section 52(c) of the Customs Act 1901.

It has been suggested that Frank Forde, the Acting Minister for Trade and Customs, had already decided to ban the book, and sought Garran's advice primarily as a buffer against political criticism.

[76] He was the vice-president of the Canberra Musical Society, where he sang and played the clarinet, and in 1946 won a national song competition run by the Australian Broadcasting Corporation.

[79] Geoffrey Sawer, the ANU Law professor, believed Garran had brought his quiet religious faith to bear in his life of service:"The Commonwealth was fortunate in having through so much of its early history the services of such a man—superbly intelligent, with great practical commonsense, a Christian both in moral rectitude and in loving-kindness, selfless, devoid of any faintest touch of arrogance, priggishness or conceit, with a sense both of humour and of fun.

"[1] His death "marked the end of a generation of public men for whom the cultural and the political were natural extensions of each other and who had the skills and talents to make such connections effortlessly.

"[61] Garran's friend Charles Studdy Daley, a long time civic administrator of the Australian Capital Territory, emphasised Garran's contribution to the early development of the city of Canberra, particularly its cultural life, remarking at a celebratory dinner for Garran in 1954 that: "There has hardly been a cultural movement in this city with which Sir Robert has not been identified in loyal and inspiring support, as his constant aim has been that Canberra should be not only a great political centre but also a shrine to foster those things that stimulate and enrich our national life... his name will ever be inscribed in the annals, not only of Canberra, but of the Commonwealth as clarum et venerabile nomen gentibus.

"[32] Former Prime Minister John Howard, in describing Garran, said: "I wonder though if we sometimes underestimate the changes, excitements, disruptions and adjustments previous generations have experienced.

"[82] At one level, Garran's remarkable career epitomises the hay day, or Indian Summer, of the meritocratic bourgeois elite born in Australia in the third quarter of the 19th century.

At another level, his exceptional influence as an eminence grise bespeaks his fluency in construction, be it in poetry translation or legislative drafts, even if always out of commonplace materials.