The Labour leader said he would be able to change the county “within months” of becoming prime minister.
In an interview with the BBC’s Sunday with Laura Kuenssberg programme, Starmer said growth was the “single defining mission for a Labour government”.
Starmer was speaking at the start of Labour’s conference in Liverpool, likely to be the last big gathering of party members before the general election.
Polls suggest he is on course to become PM, with a Survation survey published on Sunday suggesting a dozen Tory cabinet minister are at risk of losing their seats at a Labour landslide.
A separate poll by Opinium for The Observer showed Labour has actually increased its lead to 13 points since the Conservative conference.
Rishi Sunak has to call the election by January 2025 at the latest - although it is widely expected to be held in the Spring or Autumn of next year.
Starmer said he would be using Labour’s conference to answer the question: “If not them then why us?”
Asked how soon voters could expect see higher growth than the UK has had in the last ten years, and therefore more investment in public services, Starmer said: “Very quickly.
“Some of the changes we need to make can be done very quickly. We think think this can happen very quickly, within months of a Labour government, we can turn this around.”
Despite the consistent poll lead, Starmer is under pressure from some in his party to make a more bold offer to voters.
Matt Wrack, the general secretary of the Fire Brigades Union and also TUC president, told HuffPost UK the party risked being “over-cautious” .
Sharon Graham, the general secretary of the Unite union, told Sky News that “at the moment Labour have been too timid”.