Matteo Renzi, leader of the centre-left Democratic Party, is making his first visit to the UK after being sworn in as his country’s youngest premier in February.
It is the latest in a series of one-on-one discussions with EU heads of government about the priorities which should be set for the new European Commission, which is due to be appointed following the European Parliament elections next month.
Europe’s response to the latest developments in the Ukraine crisis are likely to be high on the agenda as well as EU matters.
Mr Cameron’s hope of renegotiating Britain’s relationship with Brussels was boosted when Germany agreed it must not be put at a disadvantage by eurozone nations’ moves to integrate more closely.
Wolfgang Schauble said any changes to EU treaties must “guarantee fairness” for member states outside the single currency bloc.
The declaration meets one of Mr Cameron’s key negotiating demands - that the rights of non-eurozone states must be protected - ahead of his planned 2017 referendum on Britain’s membership of the EU.
A No 10 spokeswoman said Mr Cameron’s goal of reforming the EU and renegotiating Britain’s membership will involve a “long-term conversation” involving all 28 member states.
She said: “There are signs that the debate he is leading on reform across Europe is really taking hold, with other countries coming out with issues like cutting red tape or addressing issues of the abuse of free movement.”
The leaders have previously met at EU summits.