The 10-year agreement, signed in 2014 but not implemented due to legal challenges, will see more US troops rotate through the Philippines for war games and help their hosts build military facilities.
Supreme Court spokesman Theodore Te said the accord was upheld with a 10-4 vote, ruling that President Benigno Aquino's government had the authority to sign the pact and did not need congressional approval.
Aquino negotiated the accord to help the Southeast Asian nation improve its military capabilities and draw the United States closer, partly in a bid to counter a fast-expanding Chinese presence in disputed parts of the South China Sea close to the Philippines.
US President Barack Obama also pushed hard for the Enhanced Defense Co-operation Pact (EDCA) as part of his so-called strategic "pivot" to Asia that has involved expanding American military presence in the region.
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However it faced immediate legal challenges from groups opposed to US military involvement in the Philippines, a US colony from 1898 to 1946.
The EDCA agreement was signed in April 2014 as Obama visited Manila, when he said it would give US forces "greater access to Filipino facilities, airfields and ports, which would remain under the control of the Philippines".
Filipino officials also previously said it would allow the United States to store equipment that could be used to mobilise American forces faster -- particularly in cases of natural disasters such as the frequent typhoons that batter the archipelago nation.