The 30-year-old had been a free agent, having been released by the Hammers at the start of June and will now step into the Championship as relegated QPR continue to rebuild their squad.
O'Neil will be teaming up once again with QPR boss Harry Redknapp, the duo having worked together previously at Portsmouth, for whom O'Neil made over 150 appearances between 1999 and 2007.
Having joined Middlesbrough in the summer of 2007, he went on to play over 100 times for Boro, before signing a two-and-a-half-year deal with West Ham in January 2011.
If his move to QPR is confirmed he would be following in the wake of Danny Simpson, Richard Dunne and Charlie Austin, who have already joined the west London club this summer.
QPR begin their Championship campaign at home to Sheffield Wednesday on Saturday as they look to bounce back into the top flight at the first attempt.