The deal will give Fox access to the Roku channel, first-party data and more than 100 million global streaming households.
Fox will pay $US96 in cash and 0.9693 shares of its Class A common stock for each Roku Class A and Class B share outstanding. The transaction is valued at $US160 per Roku share.
Existing Fox shareholders are expected to own approximately 73 per cent of the combined company and Roku shareholders will own about 27 per cent, once the deal closes.
The deal is expected to close in the first half of next year. It still needs approval from Fox and Roku shareholders and also regulatory approval.
"This is a defining moment for Fox, and a natural extension of the deliberate and focused strategy we have been executing for nearly a decade," Fox Corp chief executive Lachlan Murdoch said.
"In 2019, we reoriented the company around live news and sports. In 2020, we acquired Tubi and under our stewardship it has become one of the most successful businesses in streaming.
"Today, we take the next step: bringing together the most valuable live content portfolio in video consumption with the pre-eminent streaming platform through which America watches it. This combination will transform the scope of our company into high-growth verticals and yield a step change in our overall growth profile."
Fox is a media giant with a portfolio of news and sports including the NFL, MLB, NASCAR, FIFA World Cup, Fox News and Fox Business and entertainment content.