The provider is putting in place mortgage specialists, in several key branches, as part of a pilot scheme.
Initially seven mortgage specialists will be available in larger branches in Birmingham, Solihull, Walsall, Luton and Norwich.
The Post Office hopes to expand this over time and eventually have a network of hundreds of advisors.
Until now, people have had to apply online or over the phone for a mortgage with the provider, which has offered mortgages since 2009.
Currently the Post Office offers deals for people with deposits as low as 10% but has said it plans to "sharpen up" its range in the near future.
The Post Office said its new mortgage software will enable customers to find out how much they could borrow and view products and repayments on screen.
Customers can be provided with a printed approval in principle and have the opportunity to submit a full mortgage application under the plans.
Mike Cook, head of Post Office mortgages, said the provider wants to build on its reputation as a trusted brand.
He said it would take several years to achieve the ambition to become one of the top 10 largest mortgage lenders.
While there have been recent signs of a mortgage war between lenders trying to attract less "risky" borrowers with big deposits, those with smaller deposits are expected to have a tougher time finding a deal in the coming months amid the weak economy.
Mr Cook said: "Last year over 40% of our borrowers were first-time buyers, which is something we are always open to.