She is the "country's leading expert" on pensions, savings, and financial education, he said, adding he wanted Altmann "at the heart of government".
This would give people "more power to save, to access their pension, to pass their pension on to their children".
Labour, which did not comment, is focusing on immigration on Saturday.
Under the plans Altmann would be tasked with a review of financial fairness for consumers, including looking at charge caps for pension products.
Mr Cameron said the appointment would make sure "we complete this revolution where we are giving people more power to save to access their pension, to pass their pension on to their children because we want to create a real saving culture in our country for everybody, not for the rich at the top but everybody who saves and has a pension".
The Conservatives are also examining other ideas for improving banking services and competition within the sector, such as allowing customers to take their account number with them to a new bank.
Main pledges
Policy guide: Where the parties stand on pensions
Altmann said: "It's vital that ordinary savers have protection from rip off charges and from unusual practices.
"The pensions industry has relied on people not understanding what the terms are in terms of savings and it is now time that ordinary people are given fair treatment, clear and fair charges.
"What I'm really excited about is the opportunity to become a minister and to protect the public... in terms of looking after their savings, being treated fairly by the big financial companies and also rolling out financial education to younger age groups not just focusing on the people who are at the end of their saving lives."
Altmann, a former director-general of over-50s insurer and holidays firm Saga, was appointed the government's business champion for older workers in 2014.
Her website says she is a leading authority on all aspects of pensions.
Altmann was also an advisor to former Prime Minister Tony Blair.
Pensions campaigner Ros Altmann would be made a Tory peer and minister for consumer protection if the party wins the election, David Cameron has said.