The Australia international was one of several summer signings made by the Devon outfit but has missed the opening to the new Aviva Premiership campaign due to commitments to his former club the Waratahs.
However, Mumm is ready for selection for Chiefs boss Rob Baxter, and the 28-year-old is raring to go in English rugby.
"I'm really excited to get here at last and meet Rob Baxter and everyone. It has taken quite a while, and being here was more of an idea. Now it's reality," said Mumm.
"It's like my first day at a new school, but sometimes you need a change. I really enjoyed my time with the Waratahs and playing Super Rugby, but I knew I was ready to try something else. The time had come to try something new and the Premiership is certainly one of the top competitions in the world.
"It's the intensity and physicality of the competition, week in, week out. It's a war of attrition, and you have to really work hard to earn your points. I'm looking forward to getting stuck in, and it's going to be a real challenge for me. That challenge is the reason I came here."
Chiefs travel to London Welsh on Sunday.