The brief will see Chatsworth giving media relations advice and support to the international organisation and newly elected president Marshall Bailey.
A key aim will be to boost the profile of the organisation, which represents financial market professionals and has more than 13,000 international members from 60 countries.
It will also be assisting with stakeholder engagement at a critical time for the industry, which has been under significant media scrutiny.
Bailey, who was voted in as ACI president in the spring, said: "ACI International has engaged Chatsworth Communications due to its deep knowledge of the financial services industry at a time when we needed visibility.
"One of our main constituent groups, the FX market participants, has a vital role to play in global trade but reputation has taken a battering. Chatsworth will help our organisation take a lead in that debate.
"We’re working with Chatsworth because it has a pinpoint expertise in FX, capital markets and financial technology.
"We’re focusing on helping to restore trust in the role and operation of financial markets and the role technology has to play."
Chatsworth, which will be targeting broadcast, national and international press as part of the brief, currently works with FX clients including CLS Bank and ParFX.
Some individual country chapters of the ACI will continue to manage their own comms in their local markets where they have expertise.