The 29-year-old Poland international has signed his second two-year deal with United after being an ever-present this season.
Manager Jackie McNamara told the club's official website: "This extension is merited because Rado has shown that he is an excellent SPL goalkeeper.
"It can sometimes be difficult for a foreign player to come into a club and settle but he has done so superbly.
"He is a very good shot stopper and in my time here has shown some excellent aerial handling skills.
"It is a bonus for him to know his future is secure until at least May 2015 and it is great for us to know he wants to remain a United player until then also."
Cierzniak added: "I enjoy playing for Dundee United very much and, having settled in the area, it is an easy decision for me to sign on for a further year.
"I came here to improve as a player and I feel I am doing so.
"The club, players and supporters have all helped with this and I look forward to exciting times over the next few years at Dundee United."