The UK has pledged to pay 10% of the developing world's foreign debt bill in an attempt to fight poverty.
Mr Brown is on a six-day tour of Africa
Gordon Brown has signed a debt relief deal with Tanzania - and he said the UK would make similar offers to 70 poorer nations around the world.
Under the plan - which could cost the UK £1bn - countries must spend the cash saved on health, education and welfare.
"We make this offer unilaterally but we are now asking other countries to join us," the chancellor said.
Mr Brown, on a week-long tour of Africa, spent two days in Tanzania before heading on Friday evening to Mozambique, a country where more than half of the 17-million population lives below the poverty line.
There he is expected to strike a similar debt relief pact.
The chancellor said he hoped other G8 and European countries would follow suit.
"Our wish is to have 100% debt relief and we hope that America, Japan, France and other European countries will follow Great Britain in this effort," he told reporters on his arrival in the capital Maputo.
"We hope that we are in a position to get all other countries to sign up to a new package of debt relief," he added.
The UK has already cancelled its bilateral debts - money the UK alone is owed - with the world's poorest nations including Tanzania.
Mr Brown said action was now needed to tackle debts with lenders such as the IMF and World Bank.
But his proposals have met with a mixed reaction, with some critics, including former international development secretary Clare Short, questioning the effectiveness of debt relief as a means of tackling poverty.
Mr Brown said Britain would agree to pay 10% of Tanzania's repayments to the World Bank and the Africa Development Bank, which amounts to about £3.5m a year.
"What we offer to Tanzania today we offer to the whole developing world tomorrow," he told reporters in Tanzania.
"Although there is no international agreement yet, Britain will relieve those countries still under the burden of this debt by paying our share - 10% - of their payments to the World Bank and African Development Bank in their stead."
The chancellor, who is on a week-long tour of Africa, arrived in Dar-es-Salaam on Wednesday, where he has visited education and health projects.
He also travelled to the country's capital Dodoma where he visited a centre for people with HIV/Aids.
Mr Brown's pledge was welcomed by Clare Short but she said it was a "controversial" policy not backed by every country.
"If debts owing the World Bank are written off, there is less money to give to others and there are some very poor countries without debt, so you have got to be careful about being fair."
Debt relief was increasingly being seen as a "mystical solution" to poverty, "when in fact it is just the equivalent of giving aid.
"It is a good thing, but it is not world-changing," she told BBC Radio 4's Today programme.
Ms Short, who quit the government over the war in Iraq, said the biggest cause of poverty in Africa were "failed states" such as Sudan and the Democratic Republic of Congo.
"Debt relief and aid alone without really strong action to end conflict, arms supply, start building order, the basic institutions of a state, leave the poor outside the whole development system," she added.
Mr Brown is also due to visit South Africa, where he will attend a meeting of Commission for Africa, Tony Blair's organisation to boost development in the continent.
The chancellor has already unveiled proposals for a G8 aid package which he has likened to the Marshall Plan used by the United States to rebuild Europe after World War II.