The 30-year-old midfielder signed a one-year contract at Loftus Road on Wednesday after being released by West Ham United.
"The challenge here is an exciting one," O'Neil told the club's official website.
"Obviously I know Harry [Redknapp] well and he was a big factor in me coming here. The promotion season we had under him at Portsmouth was fantastic.
"He's played a massive role in my development as a player and now I'm back playing for him again and I want to repay him by helping this club get back into the Premier League."
O'Neil joins QPR having spent two years at West Ham.