Former Philippines President Benigno Aquino III, who belonged to one of the country’s most prominent political families and during his term pushed back against China’s expansive claims in the South China Sea, died on Thursday in Manila. He was 61 years old.

Mr. Aquino’s family said he died peacefully in his sleep due to “renal disease secondary to diabetes.” Tributes to the former leader, popularly known as “Noynoy,” poured out on social media on Thursday and a spokesman for current President Rodrigo Duterte offered condolences on behalf of the government.

“We’re grateful to the former president for his contributions and services to the country. Rest in peace, Mr. President,” the spokesman said.

Mr. Aquino served as Philippine president from 2010 to 2016. His administration brought an unprecedented arbitration case challenging Beijing’s claim to historic and economic rights in the South China Sea. The tribunal at The Permanent Court of Arbitration in The Hague held in a landmark 2016 decision that China’s claim had no legal basis.

Although China rejected the outcome, the decision constitutes a critical document of international law on the strategically important waterway. It is frequently cited by other governments, including the U.S., in opposing China’s actions in the South China Sea, where Beijing has built and militarized artificial islands. Mr. Aquino’s government filed the case after a 2012 standoff between the Philippine Navy and Chinese fishing vessels in which Manila effectively lost control of an outcrop called the Scarborough Shoal.

Mr. Aquino also strengthened ties with the U.S., a longtime ally. In 2014, they signed a defense pact giving the U.S. military access to a number of Philippine bases.

After Mr. Aquino left office, the Philippines’ foreign policy underwent a stark shift. His successor, Mr. Duterte, moved the country closer to Beijing and strained relations with Washington. The 2014 defense agreement is effectively stalled and an older military pact, called the Visiting Forces Agreement, is in limbo.

Both of Mr. Aquino’s parents were democracy icons and opponents of the late dictator Ferdinand Marcos. Mr. Aquino’s father was assassinated after returning to the country from exile in 1983. That was a turning point in the nation’s political history and lent momentum to the pro-democracy People Power movement that ultimately ended Mr. Marcos’ 20-year reign. Mr. Aquino’s election bid in 2010 was buoyed by popular support for his mother, former President Corazon Aquino, following her death a year earlier.

Mr. Aquino’s six-year term was defined by a tough anticorruption agenda and it ushered in a period of rapid economic growth. He largely stayed out of the political spotlight after leaving office.

Write to Feliz Solomon at feliz.solomon@wsj.com