In partnership with his brother, he bought up extensive tracts of land in the South-East of South Australia; by 1891 they owned 75,000 acres (30,000 ha) of pasture and farmland.
Their greatest asset, Glencoe station, founded by Robert Leake and his brother Edward, covered 53,000 acres (21,000 ha), and carried 53,000 sheep, 3,500 cattle and 300 horses and featured a magnificent woolshed now held by the National Trust.
[2] When the Riddoch brothers dissolved their partnership in 1898, John took the southern end and broke it up for closer settlement; George named his portion "Koorine".
He was a good friend of the poet Adam Lindsay Gordon, who was a frequent guest at Yallum, and there wrote arguably his most famous poem The Sick Stockrider.
[1] He married Eliza or Elizabeth King ( – 2 October 1881) on 12 May 1854; he was survived by a son, John Alexander Riddoch of Katnook, and three daughters.