His grandfather was Edward Hamersley (Snr); among his uncles was Edward Hamersley (Jnr) and Maitland Brown; and he was related by blood or marriage to many prominent Western Australians including John Forrest and William Locke Brockman.

He returned to Western Australia in 1889, spending some time on the Eastern goldfields, before farming with his father at York until 1895.

In 1900 he became a Justice of the Peace, and the following year he unsuccessfully contested the Legislative Assembly seat of Toodyay as an independent.

On 5 August 1904, he won the Legislative Council seat of East Province in a by-election following the death of Edward Keane.

A by-election was subsequently held on 2 September 1916, with Hamersley winning re-election on a significantly higher turnout.