McNamara, who led England to the semi-finals of the Rugby League World Cup last month, will remain in that position part-time as well as working alongside Roosters coach Trent Robinson.
"It's always been an ambition of mine to coach in the NRL and the chance to work with the NRL champions is something that doesn't come along very often," he said.
"I have a great relationship with Trent Robinson and am looking forward to working alongside him and the rest of the Roosters staff in what is a very exciting chapter in my career."
The NRL begins in early March while England's next matches will be as part of the 2014 Four Nations tournament in Australia and New Zealand in October.
- Sports & Recreation
- Trent Robinson