Appointed attorney-general of Victoria in 1899, Irvine succeeded Alexander Peacock as premier in 1902 with the backing of the National Citizens' Reform League and retained office after the 1902 state election.

He carried out democratic reforms but attracted the enmity of the labour movement for his suppression of a railway strike in 1903, resigning as premier in 1904.

He subsequently entered the King's Inns with the intent of qualifying as a barrister, but the death of his father and financial difficulties led him to instead immigrate to Australia.

Irvine struggled in his first years as a barrister, supplementing his income with work as an examiner at the law school and the authoring of textbooks on the powers of justices of the peace and women's property (co-authored with Frank Gavan Duffy).

In line with the small government principles of the Reform League, he had introduced retrenchments across the public service which had a particular impact on Victorian Railways workers.

Irvine launched a "swift and crushing" response, including the dismissal of strike leaders, forfeiture of accrued benefits, and the employment of strikebreakers.

He joined the "corner group" in parliament and clashed with Protectionist leader Alfred Deakin and Australian Labor Party frontbencher Billy Hughes on a number of occasions.

In September 1913 he survived a censure motion by only a single vote, following accusations that he had failed to deal with a conflict of interest by continuing to represent private clients while serving as attorney-general.

Robert Menzies, who argued several cases before Irvine early in his career, described him as a "first-class trial judge, dignified, upright, cold in manner […] but perceptive, and devoted to justice", while Arthur Dean stated he "presided over his court with great dignity and decorum, but with some degree of detachment from the case before him, particularly in the dangerous hours after lunch".

He was seen as "cold and aloof" by some colleagues,[1] although as acting governor he and his wife were apparently popular among the general public where he became known for his "resonant and rich speaking voice".

[2] According to the Dictionary of Irish Biography, he was "eccentric in his private habits, and often suffering from debilitating neuroses, he would go sculling and bush-walking to stave off his personal crises".

[2] A significant collection of papers relating to Irvine and his family, including his Irish nationalist uncle John Mitchel, were donated to the State Library of Victoria in 2008.