Forrest led several major expeditions into the interior in search of pasture lands, often with his brother Alexander Forrest.
Forrest held his ministry together and kept the confidence of the Legislative Assembly over a decade when there were no political parties. He dominated politics as a strong, pragmatic conservative in a time of massive growth in Western Australia. There was a large influx of population caused by the opening of the Eastern Goldfields centred on Coolgardie and Kalgoorlie and major public works were needed. Forrest championed the famous engineer C. Y. O'Connor in the expansion of the rail network, the building of Fremantle Harbour and the construction of a fresh water pipeline from the Darling Range to Kalgoorlie. Thanks to his common sense, women obtained the vote in 1899. He was committed to the cause of Federation, took a leading role in Conventions of the 1890s and defied many of his conservative supporters by securing a strong referendum victory in 1900 that took Western Australia into the new Commonwealth.
As MHR for Swan Forrest served as a Minister in various non-Labor Governments and narrowly failed to be elected leader of the federal Liberal Party in 1913. In 1918 he resigned as Treasurer in the Hughes Nationalist Government to become the first Australian peer, Baron Forrest of Bunbury. He died at sea travelling to London to take up his seat in the House of Lords.