The 24-year-old has played 25 matches for the Waratahs since debuting in 2010, but will move west to join former coach Michael Foley at the Western Australia club.
"I've got a great relationship with Foles and he's been very helpful in developing me throughout my professional career, so I was very pleased to have the opportunity to continue working with him at the Force," Alcock said.
"It's a great opportunity for me at the Force. It's going to be a fairly new team with a number of guys leaving, and it's a great opportunity to be part of something new.
"I'm really excited about being a part of that Force back row in particular. In my mind it's been one of the most dominant back rows in Super Rugby and I'm really looking forward to getting involved and hopefully learning one or two things from them.
"My goal is certainly to get into that starting team but I need to be working on what the coaches tell me to work on and doing my best to be part of that 22 in any way, shape or form."
Foley is looking forward to coaching Alcock once again and believes the Force are starting to assemble a strong squad for 2013.
"Chris is one of Super Rugby's up-and-coming players and he's been a consistent performer for the Waratahs over the past three seasons," he said.
"As we look to re-launch the side, someone like Chris will add to the competitive edge required - both on and off the field - to make the Emirates Western Force successful.
"Chris' game against the Force in Perth last year shows he'll complement the likes of (Matt) Hodgson, (Richard) Brown and (Ben) McCalman extremely well. He's a player that's hard on the ball but brings a balance to the game with his ball-carrying.
"As we look to finalise our squad ahead of the 2013 season, we'll continue to identify the best up-and-coming talent that will not only provide balance to the side, but can ensure its long-term success."