The commanding centre-back has signed on a free transfer after leaving fellow League One side MK Dons in June.
Manager Phil Parkinson told the club's website: "I'm delighted Manuel has agreed to sign. He's a good age for a centre-half and all the homework and meeting him confirmed he's a good character.
"He's a big centre-half who goes and attacks the ball, but has got good use of it with his left foot as well."
Llera, 29, made 37 appearances for the Dons last year, scoring two goals, and has signed a two-year contract with the Addicks.