Brown said the money would go into Pakistan's program to help re-establish its control over the chaotic border region, which he has identified as the source of three-quarters of the terrorist plots that have targeted Britain since 2001.
"I'm pleased today to confirm my offer of a further 50 million pounds ($83 million) to back your plans for long-term stabilization of the border areas," Brown told his Pakistani counterpart, Yousuf Raza Gilani, at a press conference in central London.
Brown said that aid being provided by Britain would go into reconstruction, education and the relocation of people displaced in the fighting.
Gilani is in London for talks with the British leader, who has lobbied the country to do more to find the al Qaeda leaders believed to be hiding out in the border region.
Brown told the BBC on Sunday that with more troops being sent to Afghanistan, Pakistan needs "to be able to show that it can take on al Qaeda."