Thomas Giles was initially the manager of George Anstey's Gum Flat Run on Yorke Peninsula, established in 1847. The sheep run was named for the magnificent stand of red gums (Eucalyptus camaldulensis) on the property, noted as the only stand of gums on the Peninsula. The remains of them still stand on the eastern edge of the parklands that surround Minlaton.

Giles arrived in South Australia with his parents, in October 1837. His father, William, was the General Manager of the South Australian Company, having succeeded David McLaren. In 1843 Thomas became manager of a Company property at Lake Albert and shortly after began his association with George Anstey and the Yorke Peninsula.

Beginning as manager of Gum Flat Run, Giles later became Anstey's partner, when the latter returned to England. Gum Flat carried at one time 44,000 head of sheep, and 350 cattle, with 330 horses. In 1859 the sheep, numbering only 30,000 at that time, yielded 350 bales of wool.

Giles was a witness before a Select Committee of the House of Assembly which was gathering evidence on the Assessment of Stock Act in 1860. He stated that he disagreed with the assessment given by George Goyder, the Surveyor General, on the carrying capacity of the land. After discussions with the Surveyor General, the capacity of the properties on Yorke Peninsula had been re-assessed but between them there had been no overall change. Giles considered the carrying capacity should be no more than 50 sheep to the mile, a figure well below Goyder's original assessment of 108 sheep per mile at Gum Flat.

Anstey and Giles leased another property on the Peninsula, Penton Vale, near Wool Bay. Penton Vale was 107 square miles compared to 167 square miles at Gum Flat. Both properties would be resumed by the government when they began surveying the peninsula from 1869, for agricultural land.

Anstey and Giles had other properties in addition to those on Yorke Peninsula including one near 'The Hummocks,' north of the head of St Vincent Gulf, and other land west of Lake Eyre.