Sunak is flying to San Diego on Sunday to discuss the procurement of nuclear-powered submarines under the AUKUS pact between the UK, the United States and Australia.
Prime Minister Anthony Albanese will join the pair for the summit, with UK ministers hoping Sunak will announce the purchase of a British-designed fleet.
While on the US west coast on Monday, Sunak will also unveil the new integrated review of defence and foreign policy, which was being updated in the wake of Russia's invasion of Ukraine.
The refreshed review will set out the UK's approach to threats from Moscow and an increasingly assertive China.
"In turbulent times, the UK's global alliances are our greatest source of strength and security," Sunak said ahead of his trip.
"I am travelling to the United States today to launch the next stage of the AUKUS nuclear submarine program, a project which is binding ties to our closest allies and delivering security, new technology and economic advantage at home.
"As we launch the 2023 Integrated Review Refresh tomorrow, this is the future we want to deliver - a UK that is secure, prosperous and standing shoulder-to-shoulder with our partners."
Sunak last week met with French President Emmanuel Macron, smoothing out relations after they hit a low point with the September 2021 signing of the AUKUS deal, which saw Australia ditch France in favour of an agreement with the UK and US.
Negotiations during the past 18 months have presented Canberra with a choice between a British or US design.
Reports suggest Australia could opt for a modified version of the British Astute-class submarine, plugging the gap until it enters into service in the 2040s with up to five American Virginia boats.
The UK hopes AUKUS will result in work for British shipyards such as BAE Systems' facility in Barrow-in-Furness, Cumbria.
Sunak's first visit to the US as prime minister comes in another crucial week for his leadership, with Chancellor Jeremy Hunt setting out the budget on Wednesday.
Defence minister James Heappey acknowledged there have been "robust" public and private clashes between the Ministry of Defence and Treasury over funding levels.
Defence Secretary Ben Wallace has been arguing for a multi-billion-pound hike to his budget.
San Diego, in the state of California, where Sunak used to live, is home to the US Pacific Fleet.
