Mr Cameron’s Conservative Party is fighting for votes in a part of the country where the opposition Labour Party has traditionally won more seats.
The prime minister and chancellor announced six pledges for the northwest at the speech in Manchester, including increasing long-term economic growth in the region, raising the employment rate, and investing in transport infrastructure.
“We are proposing to deliver the largest and most sustained investment in transport infrastructure that the northwest has ever seen,” Mr Osborne told the audience. An increased focus on the region “can add over £18bn (€23bn) in real terms to the economy of the northwest by 2030.”
The other pledges were to make the northwest a centre of scientific innovation, raise the region’s quality of life by building as many as 25,000 new homes, and giving greater local control over the regional economy to the cities and counties of the region.
Mr Osborne last year laid out a 15-year plan to create a “northern powerhouse.”
In November, he said he would devolve more power to the city, including imposing a directly elected mayor.
Mr Cameron and Mr Osborne are also backing plans for a high-speed rail line from London to the north of England and another east-west route across the region.