The 32-year-old was most recently with Ross County, playing 22 times although his season was affected by injuries. He also counts Motherwell and Aberdeen among his former clubs and has signed a contract until January 2018.
Dundee United boss Ray McKinnon told the club’s website: “Paul gives us greater strength across the defensive line. He has been patient and showed a willingness to play for United by spending quite a few weeks in training with us. That allowed us to get a good look at him and his attributes.
“I am happy that our squad has competition and quality all over the park.”