Campbell will be asked to confirm allegations that Taylor gave her “blood diamonds” as a gift in 1997.
Prosecutors say her evidence could help to link Taylor to the stones, which they say he used to fund the brutal civil war in Sierra Leone.
He denies the charges and says he has never had anything to do with diamonds.
Allegations that the rough, uncut gemstones were given to Campbell emerged in a statement by US actress Mia Farrow.
She claimed that Campbell had told her she had been given the stones after a celebrity dinner in South Africa, hosted by
former South African President Nelson Mandela.
Campbell had initially said she did not want to testify at the trial, but the court ordered her to appear or face contempt of court charges.
Her management company later released a statement confirming she would attend “to help clarify events in 1997”.
Taylor has pleaded not guilty to 11 charges at the UN-backed tribunal.
The court has spent more than two years hearing the case.
Taylor, 62, is suspected of selling diamonds and buying weapons for Sierra Leone’s RUF rebels, who were notorious for hacking off the hands and legs of civilians during the 1991-2001 civil war.
Tens of thousands of people died in the interlinked conflicts in Sierra Leone and Liberia. — BBCOnline.