Chinese policymakers have struggled to reignite growth since the end of strict pandemic health curbs in late 2022.
The world's second-largest economy is beset by a debt crisis in the property sector, persistently low consumption and high youth unemployment.
In a speech on Friday, Xi said policymakers "are planning and implementing major measures to further deepen reform in a comprehensive manner".
"We will... form a more market-oriented, legal and international business environment," he added.
"China's door will only open wider and wider, and will never be closed."
Xi has touted the promise of significant reform several times this year, and the government has already enacted measures in key sectors such as real estate to try to address critical issues.
On Thursday, it was announced that the delayed Third Plenum -- a meeting historically watched for signs on economic policy direction -- will take place in Beijing in mid-July.
The key meeting of top officials, originally expected last autumn, is highly anticipated in the hopes it might resolve the uncertainty that has weighed on the country's economy.
Xi's address at Beijing's opulent Great Hall of the People, delivered in front of a high-profile international audience, marked the 70th anniversary of some of China's foundational diplomatic tenets.
The Five Principles of Peaceful Coexistence include mutual respect for territorial integrity, mutual non-aggression, mutual non-interference in internal affairs, equality and cooperation for mutual benefit, and peaceful coexistence.
In his speech, Xi hailed China as a force for global peace, saying Beijing would continue to play "constructive roles" in international conflicts such as Gaza and Ukraine.
China has been criticised by Ukraine's allies for failing to condemn Russia's 2022 invasion and accused of favouring Moscow. Beijing insists it is a neutral party.
In the Middle East, China has advocated for decades for a two-state solution to the Israel-Palestinian conflict.
In his speech, Xi called for greater cooperation between China and developing countries.
"Engaging in small yard, high-wall decoupling practices is to move against the tide of history," Xi said.
"It will only harm the common interests of the international community."
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