The judges, sitting in The Hague, Netherlands, convicted Taylor, 64, of aiding and abetting in the commission of 11 war crimes or crimes against humanity during overlapping wars in Liberia and neighboring Sierra Leone.
Taylor, who had pleaded not guilty, stood with his hands clasped in front of him as the court read the list of offenses, including acts of terrorism, murder, violence to life, rape, sexual slavery, outrage of personal dignity, cruel treatment, inhumane acts, use of child soldiers, enslavement and pillaging, The Guardian reported.
He is the first sitting or former head of state judged by a U.N.-backed war-crimes court for conduct considered so treacherous as to be illegal.
The court adjourned, scheduling a hearing for May 16, during which Taylor will have 30 minutes to speak. Sentencing is scheduled for May 30.
After four years of hearings at the Special Court for Sierra Leone, the court found the one-time guerrilla leader provided support for rebels during their horrific reign in Sierra Leone.
The court found from 1996 to 2002, the rebel Revolutionary United Front committed crimes that terrorized civilian populations, including murder, rape, sexual slavery and forced amputations in Sierra Leone.
Judge Richard Lussick of Samoa said more than a thousand children had the letters 'RUF' carved into their backs to prevent them escaping. Children were used to amputate limbs, guard diamond mines and hunt for food. Some were involved in fighting.
The judge said Taylor told RUF commanders to seize and hold the diamond mines in Sierra Leone so that he could trade the precious stones for arms and ammunition.
The court has also found that Taylor knew as early as August 1997 about the rebels' reign of terror in Sierra Leone and had covertly fueled the conflict by providing arms and ammunition to the RUF, helping to undermine peace efforts.
The court said Taylor received "blood" or "conflict" diamonds from the rebels that were sometimes used to buy arms and ammunition, the BBC reported. Diamonds from Sierra Leone are of better quality than those mined in Liberia.
Prosecutors had alleged Taylor used his power as president of Liberia to advise and provide resources and weapons to Sierra Leone's rebels, whose 1991-2002 uprising he considered similar to the guerrilla movement he led in his own country.
The three most senior surviving Revolutionary United Front leaders -- Issa Sesay, Morris Kallon and Augustine Gbao -- were convicted in February 2009 of war crimes and crimes against humanity.
Among those who testified during Taylor's trial was supermodel Naomi Campbell, who told the court she received "blood diamonds" from Taylor's aides.
An estimated 50,000 people were killed in the 11-year civil war, which ended after the British Armed forces, with help from the United Nations and Guinean air support, defeated the RUF.