The agency fought off tough competition to be appointed by the Business Finance Taskforce, comprising six major banks co-ordinated by the British Bankers' Association.
The group was launched in October to improve relations with SMEs, amid fears that the cost of borrowing is prohibitively expensive for many.
Portland, better known for its lobbying work and founded by Tony Blair's deputy comms director Tim Allan, will run the b2b and corporate media relations account to promote the message that the banks' 'doors are open' to small businesses.
The brief will see the agency enter into dialogue with SMEs to help explain the changes happening in the way banks approach lending and financing companies and how these businesses can best access this funding.
A key message will be the industry’s commitment to ‘responsible’ lending and that banks’ commitment to increase financing to SMEs must not impact the quality of the loans the industry issues.
A spokeswoman at the BBA said: ‘The Business Finance Taskforce is a major initiative aimed at helping business access the finance it needs. Funds and help are out there and the banks need Portland to get the message out to firms that our doors are open.
Portland beat Open Road, Fishburn Hedges and Bell Pottinger to the initial six-month contract, understood to be worth £200,000. It is thought as many as ten agencies submitted proposals.
The taskforce is comprised of Barclays, HSBC, Lloyds Banking Group, RBS, Santander and Standard Chartered.
Earlier this month those same banks, with the exception of Standard Chartered, singed up to Project Merlin, agreeing with the Government to lend £190bn to businesses in 2011, including £76bn to small firms.