Ople, who was 76, died in a hospital in Taiwan after his flight to Bangkok from Tokyo, where he had been attending trade talks, was diverted.
His brief tenure as a senior Cabinet figure began in July last year when President Arroyo plucked him from the Senate, where he held positions in several committees, overseeing some 110 international and bilateral treaties.
But his biggest legacy will be his 1999 sponsorship of a Senate resolution ratifying the RP-US Visiting Forces Agreement that allowed for the resumption of large-scale joint military exercises.
The accord was to eventually lead to the deployment of hundreds of US troops to help train Filipino soldiers against the Muslim Abu Sayyaf separatist rebels in the southern Philippines as part of an emerging global war on terrorism.
The Abu Sayyaf, a small group of self-styled Islamic militants blamed for a rash of kidnappings and bombings in the South, has been linked by Washington and Manila to Osama bin Ladens al-Qaeda network.
Ople also supported the US-led invasion of Iraq, and had campaigned for the deployment of a small Filipino contingent there.
At various times, Ople had worked as a newspaperman, public relations practitioner and a university lecturer. At the time of his death, he wrote a column for the Manila Bulletin and was a contributor to academic journals.
Singapores Foreign Minister S. Jayakumar said he was saddened by the demise of Ople, whom he described as a good friend.
"He was a senior statesman with a long and distinguished record of service for the Philippines and ASEAN," Jayakumar said, noting that Ople was due for a visit in Singapore in January.
"His passing is a deep loss for his country and the region," he added.
Ople also framed the countrys labor code and worked to promote labor rights as a minister during the dictatorial rule of Ferdinand Marcos, who was ousted by a popular revolt in 1986.
Former president Corazon Aquino, who succeeded Marcos, appointed him as a member of the panel that revised the Constitution in 1986.
Ople was first elected senator for a six-year term in 1992 and re-elected in 1998 for a second term before he was tapped by Arroyo to join her Cabinet.
Ople was taken ill late Saturday while on a Japan Asia Airways flight to Bangkok. The Philippine foreign ministry said he was en route to Bahrain, ahead of an official visit there by Mrs. Arroyo.
The flight was diverted to Taipei, but Ople was said to have died after he was taken to Minsheng Healthcare, a hospital in the northern Taoyun county, for emergency medical treatment.
His family said Ople "experienced difficulty in breathing and subsequently lost consciousness" and that efforts to revive him on board the plane and in the hospital proved futile.
Sources close to the family, however, said Ople suffered a heart attack. A chain smoker, Ople had a mild stroke in 1994 and has been suffering from a weak heart since. AFP