The Israel centre back passed his medical at Chelsea before signing a four-year deal worth £65,000 a week.
Ben Haim said: "I feel fantastic to be part of this amazing club. The first games in the Champions League, I'm very excited about that.
"If you ask every player, they want to play for Chelsea. They are one of the best teams in the world, so I'm happy to be part of that.
"Hopefully I won't disappoint anybody, especially myself. I'm sure that everything will be OK and I can't wait to start."