Former Philippine president Gloria Macapagal Arroyo has pleaded not guilty to an electoral fraud charge at the opening of a landmark trial that is seen as a key test of her reformist successor's campaign to stamp out corruption.

Arroyo, president from 2001 to 2010, is accused of rigging the results of senatorial polls in 2007 to favour her candidates. The electoral sabotage charge is the first of several criminal cases being prepared against her.

"Not guilty," she told the court in a soft voice and with a stoic expression after her defence team waived a full reading of charge details. If convicted, she could face life in prison.

The stakes are high for both Arroyo and President Benigno Aquino III.

Mr Aquino risks losing public support if she is acquitted and his rallying cry of "no corruption, no poverty" may fizzle out as just another failed attempt to fix the graft and poor governance that have hounded the nation for decades.

Arroyo's acquittal would vindicate a former leader who has portrayed her prosecution as a political vendetta to destroy her reputation and mask Mr Aquino's failure to improve the lives of Filipinos, a third of whom lives on one US dollar a day.

"Despite the continuous and massive vilification campaign against me and my family, I have always said that I will dispute all charges in the proper forum," Arroyo said in a statement, adding she wants to clear her name.

She promised to respect the law and said she expects the same from the country's leaders.

The electoral fraud case against the former president centres on a corrupt southern Philippine region where all 12 of Arroyo's Senate candidates swept all the votes and no opposition candidate won. According to the charges, there are witnesses who said Arroyo gave instruction to rig the vote in collusion with a powerful political clan leader, Andal Ampatuan Sr.

Ampatuan is on trial facing murder charges in connection with the 2009 politically motivated massacre of 57 people, including 32 journalists and opponents. He has pleaded not guilty.