Newstate Partners was set up last year, but boasts a team with more than 30 years' specialist experience in advising states and government-owned institutions on finances.
Most notably, the firm recently advised the Government of Antigua after it was forced to refinance its debt following the collapse of Sir Allen Stanford's financial empire.
Current clients include Russia, Democratic Republic of Congo and St Kitts & Nevis.
Maitland is the firm's first retained PR agency and was appointed without a pitch.
Consultant William Clutterbuck will lead the account.
The agency will target business and specialist finance publications to raise awareness with international investors, intermediaries involved in sovereign transactions and finance ministers.
Jill Dauchy, a partner at Newstate, commented: 'The globalising economy has meant that holders of all forms of sovereign debt vary greatly, with differing value and time expectations.
'Newstate is the only specialist independent advisers with decades of experience in providing financial advice to governments and state-owned corporations.'