Dr Williams served porridge to people at a parish church in Malawi There have been reports of violence between rival factions of Anglicans ahead of the archbishop's two-day stay in the country.
Dr Williams has also asked to meet Zimbabwean President Robert Mugabe.
Dr Williams hopes to address the issue directly with Mr Mugabe despite warnings it could give the president an opportunity to make political capital.
The service was moved to the stadium after the city's Anglican cathedral was taken over by a renegade bishop, BBC religious affairs correspondent Robert Pigott said.
The archbishop is also due to visit grassroots church projects caring for orphans and HIV sufferers.
The Church in Zimbabwe has been bitterly divided since 2007, when the former Bishop of Harare Nolbert Kunonga separated from the Anglican communion amid rows over the ordination of gay priests and the policies of Zimbabwe's governmentDr Williams expelled Mr Kunonga - a staunch supporter of Mr Mugabe - but Zimbabwe's courts ruled the ousted bishop should retain control of church buildings in the capital.
Tear gas has been fired into churches which have remained loyal to Dr Williams, and churchgoers have been beaten as they have taken part in services.
Critics have accused Mr Kunonga of using people loyal to President Mugabe's Zanu PF party to carry out the attacks.
The country's violent regime has come under criticism from the Church in the past.
In 2007, the Archbishop of York, Dr John Sentamu, cut up his clerical dog collar in protest at Mr Mugabe's regime, saying he would not wear it again until the president had left office.
The archbishop's nine-day tour started in Malawi on Thursday, where he marked the 150th anniversary of its branch of the Anglican Church. He also visited Church initiatives, including a Mothers' Union literacy circle.
Dr Williams' spokeswoman has said he aims to "show solidarity" with fellow Anglicans and their bishops who serve the community despite "disruption, intimidation and even violence".
The archbishop closes his tour in the city of Kitwe, in Zambia's copper belt, where he will preach at another outdoor Eucharist and attend a national clergy conference.