The 35-year-old defender, signed from Glasgow Rangers by former manager Bryan Robson last January, struck the game's decisive moment as the Lancashire side slumped to their sixth defeat in seven games.
The Deepdale side caught United on the counter attack, exposing the Sheffield back four twice in quick succession and almost snatched the lead.
Midfielder Chris Sedgwick broke up the right flank, slipped past Gary Naysmith and sent over a teasing cross.
Stephen Elliott tried to hook the ball past Paddy Kenny but miscued from ten yards.
Jon Parkin tried his luck with a right-foot shot on the turn which was snatched on the line by the diving keeper before United penetrated the Preston rearguard.
Anthony Stokes, who is on loan from Sunderland, teased his marker before unleashing a low strike from 18 yards which was scooped up by Andrew Lonergan.
The Sheffield side then threw away a golden chance to break the deadlock.
Stokes split the Preston defence with an inch-perfect pass to Danny Webber, but his first touch was poor as he raced into area and Lonergan raced off his line to snatch the ball at the striker's feet.
United swept ahead in the 51st minute after Brian Howard's free-kick was pushed out by the diving Lonergan to Webber.
His cross was met by Ehiogu, who hammered the ball in off the bar after his first strike was blocked by Youl Mawane.
Stephen Quinn hammered a low strike wide of the far post and Webber almost snatched a second with an in0swinging cross which was tipped from under the bar by Lonergan as United tried to kill off the Lancashire side.