Dr Jeevun Sandher says the spending review is a "crucial moment" for the Labour Party, and is all "about making us better off".
The Labour MP, who sits on the Commons Treasury committee, says that Britain has faced the "most serious and difficult times in almost a century".
He tells Sky News: "These are the most serious times for any government in this century, we have to rise to the challenge, and part of rising to the challenge in a democracy is being honest with people about where we stand."
Addressing the chancellor's spending review directly, Sander says Rachel Reeves is making long-term investments for the future.
He adds: "We're making decisions today, yes making people better off in the short-run, but also years to come, decades and even generations."
No ministers are speaking to the media this morning, as the government prepares for the spending review.
The cabinet will be meeting at 9.30am to rubber stamp the review, before the full details (few of which haven't already been trailed already) will then be announced in the Commons at lunchtime.