The Montfort team, led by senior consultant Nick Bastin, includes founding partner Gay Collins, senior consultant Claire Lewis – who joined the firm last spring – and consultants Shireen Farhana and Jack Roddan.
It will work with BNP Paribas Asset Management to enhance the firm's reputation in the UK market.
BNP Paribas Asset Management has assets under management valued at €436bn at the time of writing.
The business has four investment divisions: equities, fixed income, private debt and real assets, and multi-asset, quantitative and solutions (MAQS), providing services to individual savers, companies, and institutional investors.
Montfort said sustainability is "at the heart of [the client's] strategy and investment decision-making process", and the business is "making an active contribution to energy transition, environmental protection and the promotion of equality and inclusive growth".
Bastin said: "BNP Paribas Asset Management is a highly successful and ambitious business that is committed to using strategic communications to elevate its UK profile to its full potential.
"We are looking forward to working with the communications team and wider business on some really exciting campaigns this year."