After his training, Duthie was for some years travelling in Scotland and Ireland for a Sheffield firm.

Until 1887 or 1888, Duthie retained an interest in the Wanganui business, which he then sold to his partner, James Thain.

[2][7] Duthie, a conservative politician who was never sympathetic to the ideas of the Liberal Party,[8] was first elected to the three-member electorate of City of Wellington in the 1890 general election, when he came second, with 50 votes behind George Fisher, but 300 votes ahead of Kennedy Macdonald.

[2][10] Duthie retired at the end of the term of the 12th New Zealand Parliament in 1896 and did not stand in the 1896 general election.

[12][13] Duthie retired at the end of the term of the 13th New Zealand Parliament in 1899 and did not stand in the 1899 general election.

[9][14] Duthie stood once more in the three-member Wellington electorate in the 1902 general election and came second, and was thus returned alongside John Aitken and George Fisher.

[17] Duthie was remembered as one of the sternest critics of the Liberal Government under Richard Seddon.

[8] Under William Massey's Reform Government, Duthie was appointed to the Legislative Council on 26 June 1913 and served until his death.

[8][9] The Duthie family lived in Wellington until their new home, Balgownie, was completed in 1903 in the Lower Hutt suburb of Naenae.

The house, built entirely from native timbers, was at the time regarded as one of the finest in the Wellington region.

[1] Three of their daughters died young: Laura (1 September 1875 – 30 March 1876) was buried at Wanganui, while Isabella Miller (15 March 1867 – 12 November 1896; wife of Thomas Miller[19]) and Florence (27 January 1876 – 21 December 1896) were both buried at Karori Cemetery.