Campbell, 40, admitted last week that she received uncut stones from two men in South Africa in 1997 but said she didn't know they were diamonds or that they were linked to Taylor.
Farrow, 65, said Monday that Campbell in fact boasted that the gift was from Taylor at a breakfast the next day as both women prepared for a charity event with Nelson Mandela, Britain's Telegraph reports.
"Naomi Campbell joined us and before she even sat down she recounted the events of the [previous] evening," the actress testified. "She said that in the night she had been awakened. Some men were knocking at her door. They were sent by Charles Taylor and they had given her a huge diamond. Naomi Campbell said they came from Charles Taylor."
Taylor, 62, is accused of supplying Sierra Leone insurgents with weapons in exchange for illegally mined diamonds. The alleged gift to Campbell is critical to the case being presented by United Nations prosecutors at the trial in the Netherlands. Taylor has denied owning or trading in any illegal diamonds.
Campbell had sought to avoid testifying in the trial, saying she feared for her safety, but was subpoenaed and forced to appear.