Andy Burnham said his government would be "grounded in fiscal responsibility" as his first Prime Minister's Questions took place against a backdrop of rising UK borrowing costs.
Conservative leader Kemi Badenoch called on Burnham to say where spending would be cut and how he would deal with the UK's increasing debt, after the cost of borrowing for the UK reached a new 18-year high on Wednesday.
He blamed the previous Conservative government, saying the "turbulence on global markets are because of that exposure that they left behind".
Burnham took over from Sir Keir Starmer in July before Parliament's summer recess, making Wednesday the first time he had faced the Tory leader at PMQs.
Burnham sought to stress his administration's fiscal responsibility and said ministers were taking steps to reduce debt.
He told MPs: "This will be a government grounded in fiscal responsibility. It will stick to the fiscal rules, but at the same time, we will help reduce cost-of-living pressure on our constituents, and that's the approach that we will take."
Interest rates on government bonds have been going up, with the yield on a 10-year bond at its highest level since 2008, while the yield on a 30-year bond is at its highest since 1998.
This means it costs the government more to borrow over the long term and could constrain the government's spending choices as the 28 October Budget approaches.
Burnham's PMQs debut came after he used the summer recess to tour the UK, announcing a series of eye-catching policies mainly aimed at tackling the cost of living.
On Wednesday, Badenoch said the prime minister had set out plenty of spending plans but no detail of how he would be paying the bill.
"The markets are clearly worried that we now have a spendthrift prime minister who wants to say yes to everyone but cannot tell us where the money is coming from," she said.
"He needs to pay for all his new promises and he has a choice – higher taxes, more borrowing, or spending cuts.
"Yesterday he said change begins with honesty, so will he be honest and tell us: is he preparing to raise taxes again, yes or no?"
Burnham had earlier said he had already cut taxes, including VAT on energy bills and a cut in business rates for hospitality.
"I've already indicated my first moves were to cut tax, but I'm not going to do what any prime minister has done and write the budget here," he said, adding he and Chancellor John Healey had agreed on an earlier date for the Budget to reduce speculation.
