Villa boss O'Neill delighted with capture of Chelsea's Sidwell
The midfielder is believed to have received a large kickback from the £5m transfer in lieu of the pay cut he has taken after giving up a £65,000-a-week salary at Stamford Bridge which would have smashed Villa's pay structure.
O'Neill was delighted to have added his first new face of the summer, saying: "He is of the right age, and I believe the right quality, to take Aston Villa forward.
"For whatever reason, it didn't work out for him at Stamford Bridge. But he remains hungry to do well and to prove himself and I'm delighted to have him with us."