The 38-year-old former Wales international recently revealed his dissatisfaction at losing his first-team place at the Premier League club following the appointment of Gary Megson as manager.
"I tried to get Gary before the season started but Bolton wouldn't release him," Blades boss Bryan Robson told the club's official website.
"Since then I spoke to (former Bolton boss) Sammy Lee before deadline day and then Gary Megson but got the same answer so it has been an ongoing thing.
"He's a very experienced player, a 'youthful' late 30s type whose knowledge will be invaluable to us.
"He will come into the squad for Wolves and I have no doubt about his fitness levels.
"He was in Bolton's European team recently when they got a good result, and then against Liverpool, so he doesn't come here needing games to get going."