RES will help with the Front End Engineering Design (Feed) and procurement for the project. The developer has yet to make a final investment decision on it.
Project director at RES, Adam Morrison, said the firm is lending its staff and expertise to the project.
"We're helping them to manage the interfaces between different packages, prepare technical specifications to go out to tender for major parts of the plan.
"Then we will assist with those tender processes and any technical due diligence Moray Offshore is doing ahead of taking an investment decision for the project," Morrison said.
Moray Firth is made up of three projects, each using 62 turbines and a capacity of up to 372MW.
It will be located 22 kilometres from the Scottish coast in the same region as the 750MW Beatrice project. It is expected online in 2020.
Moray Offshore Renewables is a joint venture between EDP Renewables and Repsol Nuevas Energias UK formed to develop the UK Round Three project.
EDP Renovaveis and Repsol chose the Port of Cromarty Firth as the service base for the development in July.