The appointment of Prince Khaled bin Salman to Washington signals the kingdom's eagerness to strengthen bilateral ties under President Donald Trump. As the king's son, the prince has a direct line to the Saudi monarch.
Saudi Arabia is the world's third largest defence spender. Prince Khaled's appointment positions him as an influential broker in deals with US manufacturers.
Saudi-US relations had cooled under the Obama administration after Washington pursued a nuclear accord with Shiite-ruled Iran that the Sunni-ruled kingdom strongly opposed. Saudi Arabia and Iran are regional rivals, and back opposing sides in the wars in Syria and Yemen.
Saudi Arabia was quick to praise Trump's missile strike on a Syrian military base in response to an apparent chemical weapons attack on civilians.
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Prince Khaled is a former F-15 pilot who graduated military-aviation training from Columbus Air Force Base in Mississippi in 2009 and took part in anti-IS strikes in 2014 as part of the US-led coalition.
He also participated in flight missions over Yemen, where the kingdom has been bombing a Yemeni faction aligned with Iran for more than two years.
He has been an adviser at the Saudi Embassy in Washington since late last year.
US officials say the Trump administration is considering ways to boost military support for the Saudi-led fight against Iran-backed rebels in Yemen. The US already is helping the Saudis with intelligence and logistical support for the bombing campaign in Yemen, and could assist with greater intelligence support to counter Iranian influence there.
Days before being relieved of his post in Washington, Prince Abdullah published an op-ed in the Wall Street Journal calling for continued US resolve to end the conflict in Syria.
He said Saudi Royal Air Force jets operating out of a base in southern Turkey have conducted more than 340 strikes against Islamic State targets in Syria since February.