With the UK facing the prospect of leaving the European Union, the SNP minister told Philip Hammond it was “the wrong time for austerity”.
Additional spending cuts at this time could be “disastrous”, Mr Mackay added.
But the UK Government says Scotland will benefit from additional cash, to be allocated through the Barnett formula, as a result of “significant investments” by the Chancellor.
Spending in areas such as education and skills south of the border will give the Edinburgh administration an “important uplift in its budgets”, with the Treasury adding this will build on £800 million for Scotland as a result of decisions in the Autumn Statement.
However, Mr Mackay said: “The cuts already planned by the UK Government mean that by 2019-20, the Scottish Government’s discretionary budget will be £2.9 billion (9.2%) lower in real terms than it was in 2010-11.
“Any change in spending must be seen against the context of the huge cuts we are already facing.
“The Chancellor has an opportunity in his budget today to offer some much-needed financial relief for households and public services.
“The UK Government plan for an additional £3.5 billion of spending cuts in 2019-20, at precisely the point when the UK’s departure from the EU could occur is disastrous.
“I say clearly to the Chancellor - this is the wrong time for austerity.
“We need to see investment and support for economic growth from the UK Government at a time when Brexit poses a self-inflicted and unprecedented risk to the UK economy, public finances and consumer confidence.”