The assembly government will have around £200m more than expected to spend this year.
The Treasury has announced it will give Welsh ministers access to money not spent in previous years.
Wales' Finance Minister Jane Hutt had been pressing for the money to be made available.
The assembly government must still make £163m in savings this year, although it has the option to defer the cuts until next year.
Welsh Secretary Cheryl Gillan welcomed the Chief Secretary to the Treasury's announcement which will allow the assembly government to access around £200m of so-called "end year flexibility" (EYF) cash.
The £200m comprises unspent cash accumulated from previous assembly government budgets.
Mrs Gillan said: "Following the review it is clear that we have to tighten access to EYF but, in keeping with the respect agenda, the Welsh Assembly Government will be able to access specific EYF stocks this year.
"This means that despite the huge budget challenges we face, we have been able to provide the Welsh Assembly Government with access to around £200m of EYF money this year.
"I know this will be of considerable benefit to public services in Wales."
The assembly government has to find large savings this year as part of its share of the £6.2bn cuts announced by the Treasury earlier in the year.
It can defer the £163m savings required but, with even bigger cuts coming in 2011-12, ministers may decide to use the windfall to pay off this year's cuts.
Meanwhile, the Welsh budget will not be affected by Monday's announcement of £1.5bn of unfunded spending commitments being cut in several Whitehall departments.
The Treasury said since the plans were unfunded, there was not any money due to come to Wales anyway.