Trident will pay an unnamed private Australian company A$8 million for the royalty, which CEO Adam Davidson said would become a "cornerstone asset" for the company.
Lake Rebecca, outside Kalgoorlie, has a resource of 1.035 million ounces.
Drilling highlights since February included 40m at 5.06gpt gold, 19m at 5.90gpt gold, 12m at 6.73gpt gold and 51m at 2.90gpt gold.
"We are delighted to announce the acquisition of the royalty over Lake Rebecca which will provide our shareholders with precious metals exposure from a significant and growing asset in the world's top mining jurisdiction," Davidson said.
"Existing, uncapped gold royalties over attractive, substantial gold projects being developed by credible operators are incredibly scarce globally, let alone in a jurisdiction such as Australia which more traditionally utilises equity and debt markets for project finance.
"At this early stage, Trident believes that Lake Rebecca is on track to support a circa 100,000ozpa operation, located in a desirable jurisdiction being supported by gold prices at close to all-time highs."
Trident debuted on AIM in June with a £16 million initial public offering.
Its first acquisition was a 1.5% free-on-board revenue royalty on part of Mineral Resources' Koolyanobbing iron ore mine in WA. This was followed by a 1.25% gross revenue royalty on the Mimbula copper mine in Zambia operated by Moxico Resources, a scaling gold royalty on the Spring Hill gold project in Australia operated by PC Gold, and a portfolio of four exploration and development stage gold royalties in WA from Talga Resources.