"We shall continue to devote the increasing weight of our resources to the prevention and control of serious crimes, rather than take the lives of those who commit them," Gloria Macapagal Arroyo said on Saturday.
Noting that she was signing the law a day after a car bomb killed six people in a southern Philippine province, Arroyo said, "We will never be intimidated by these treacherous acts, and we shall fight terror as seriously as we embrace peace and development, solidarity among our law-abiding citizens and our strategic alliances."
She called on law enforcers, judges, prosecutors and communities to help shoulder the responsibility of "sharpening law and justice for all."
Papal Nuncio Archbishop Fernando Filoni, the Vatican's envoy to Manila, congratulated Arroyo and legislators who approved the measure.
"This could be another very important nice step to go on in showing that the culture of life is very alive and important in this country," Filoni said. "We cannot speak about human rights when death penalty is imposed."
Arroyo signed the law shortly after returning to the presidential palace from a hospital where she was taken late on Thursday, suffering from acute diarrhea.
Congress two weeks earlier approved a bill abolishing capital punishment despite protests from anti-crime activists, who think Arroyo, a staunch Roman Catholic, rushed its approval to please the pope.
The lethal injection chamber at
New Bilibid Prison south of Manila
Arroyo was set to leave for the Vatican on Sunday. She is scheduled to meet with Pope Benedict XVI.
The Philippines' 1987 constitution abolished the death penalty, which the government of late dictator Ferdinand Marcos used to execute about a dozen people convicted of rape and drug charges.
Congress restored the death penalty in late 1993 for crimes such as murder, child rape and kidnapping. Seven people have been executed since then.