The 32-year-old said that McNamara has fostered an excellent team spirit within the camp with regular get-togethers.
"I think the beauty of the current England set-up is that there are so many leaders in the group," Sinfield told Sky Sports News. "Because of what's been created in the last 24-30 months by Steve, there's a lot of togetherness in the group.
"It's not like you're going in there and you've got to pull 30 guys together and make sure you're going in the right direction, all that prep has been done now. The lads go in and the togetherness is there straightaway."
Sinfield has played 18 times for England.