Reuters said the verdict will be the first passed on a former head of state by The Hague's international courts in what human rights advocates say is a reminder that even the most powerful do not enjoy impunity.
The one in Taylor's case, the first test of international justice against a former head of state, will be watched closely in much of Africa and beyond.
Taylor, who was president of Liberia from 1997 to 2003, is accused of backing and giving orders to Revolutionary United Front (RUF) rebels in the 11-year civil war in neighbouring Sierra Leone that killed some 50,000 people.
The prosecution says the RUF undermined a ceasefire agreement in 1999, prolonging the war for another three years, and that Taylor financed their war effort from the proceeds of "blood diamonds" mined illegally in Sierra Leone.
"The Taylor verdict is a watershed moment, however it turns out," said Richard Dekker, head of the international justice programme at Human Rights Watch.
"As president, Taylor is believed to have been responsible for so much murder and mayhem which unfolded in Sierra Leone. His was a shadow that loomed across the region, in the Ivory Coast, in Sierra Leone and Liberia," Dekker added.
Taylor has denied the charges.
"The trial chamber finds you guilty of aiding and abetting of all these crimes," AFP news agency quoted presiding judge Richard Lussick as saying at the Special Court for Sierra Leone.
The verdict was the first against a former head of state by a world court since the Nuremberg trials.