Prime Minister Sir Keir Starmer will give his backing to the chancellor's Budget in a speech on Monday, and commit the government to going "further and faster" on pro-growth measures.
He will say Chancellor Rachel Reeves's statement will help to alleviate cost of living pressures, lower inflation and ensure economic stability.
It comes as the Treasury faces questions over whether it was transparent about the state of the public finances in the run-up to the Budget.
The Conservatives claimed Reeves misled the public by being too pessimistic about the economic outlook when official forecasts painted a more upbeat picture.
No 10 has denied that Reeves misled voters and defended her statement.