Sri Lanka has rarely, if ever, topped any U.S. foreign-policy agenda. But after the surprising outcome of its presidential election earlier this month, it should get higher billing.

In a stunning reversal, Sri Lankans ousted President Mahinda Rajapaksa after 10 years of increasingly authoritarian and corrupt rule. By the time of the election, Mr. Rajapaksa had effectively turned the nation into a family-owned business, with seemingly little room for political opposition and scant attention to the reconciliation and accountability needed by all Sri Lankans following the violent, decades-long fight against Tamil separatists. The Rajapaksa family’s grip on the country made the election outcome all the more surprising.

In his place, Sri Lankans voted in a diverse coalition of parties led by Maithripala Sirisena, the former general secretary of Mr. Rajapaksa’s own Sri Lanka Freedom Party. Mr. Sirisena ran on a platform of constitutional reforms to limit executive power and restore independent oversight bodies. He also presented a more cautious view of Sri Lanka’s increasingly close relationship with China, which over the years bankrolled the Rajapaksas’ self-interested infrastructure projects, such as the strategic deep-water port in Hambantota.

Sri Lanka’s dramatic and peaceful nod to democracy should not be overlooked. Sri Lankans now have a choice with whom to engage, and China needn’t be their only friend. The U.S. should move quickly to take advantage of the opening presented by the newly elected government.

A good first start would be to invite President Sirisena to Washington to show support for an agenda that includes ethnic reconciliation, restoration of the country’s democratic institutions and a broader Sri Lankan foreign policy. An early invitation to the new Sri Lankan leader would demonstrate Washington is ready to turn a new page with Colombo and allow the U.S. to encourage Sri Lanka to respond to the United Nations’ concerns.

It’s also a good time for U.S. businesses to take a fresh look at investing in Sri Lanka. According to the Heritage Foundation-Wall Street Journal’s 2015 Index of Economic Freedom, Sri Lanka has one of the most open business environments in South Asia. As a global leader in garment manufacturing, Sri Lanka is making the transition to middle-income status and has raised per-capita income during the past decade to $3,300 per person from $1,000.

The U.S. already is Sri Lanka’s most important trading partner. But it can increase its economic engagement through investment in infrastructure projects, especially in the war-torn areas of the north and east.

The Sri Lankan military deserves high marks for staying out of the democratic process. But the institution is in need of reform. To encourage those efforts, the U.S. should consider reviving military-to-military contacts, which Washington drastically reduced in 2008 because of human-rights concerns.

The U.S. should also coordinate with like-minded nations, such as Japan and India, in shoring up the new government and reinforcing its initial policy moves. The new leadership has signaled its interest in departing from Mr. Rajapaksa’s pro-China policies, yet Washington, New Delhi and Tokyo must reciprocate quickly to offer concrete opportunities for engagement.

While human rights and national reconciliation should remain priorities for the U.S. government, Washington must show strategic patience as the new government attempts to implement changes, such as carrying out recommendations of the Lessons Learnt and Reconciliation Commission. Mr. Sirisena has pledged to address minority grievances. But he must be given the opportunity to live up to his words.

Now is the time for the U.S. to develop a roadmap for reviving ties with Sri Lanka that reflects the broad array of U.S. interests, including respect for human rights, democracy and the rule of law, as well as enhancing trade and regional economic integration and securing the Indo-Pacific.

Without plans for restoring U.S.-Sri Lankan relations, Washington risks losing an opportunity to deepen ties with a strategically located island nation of 21 million people. Sri Lankans have taken a major step forward in re-establishing democracy. Under Mr. Sirisena, the country stands to remove itself from China’s Indian Ocean “string of pearls.”

Editor’s Note: This commentary was co-authored by Richard Armitage and Kara Bue.

 - Mr. Armitage was deputy secretary of State from 2001 to 2005.

 - Ms. Bue was deputy assistant secretary of State for political military affairs from 2003 to 2005.

 - Ms. Curtis is Senior Research Fellow at The Heritage Foundation.