Beattie, a £4million summer signing from Everton, converted from the penalty spot 12 minutes from time after substitute Sean St Ledger was adjudged to have handled in the area.
Darren Carter had put Preston ahead with a first-half free-kick and United had looked short of ideas until referee Jarnail Singh pointed to the spot following St Ledger's challenge on substitute Danny Webber.
The result leaves North End without an away victory this season and extends United's winless run to six.
Preston, who reverted to the XI which began the 5-1 win over Southampton on October 2 after Matt Hill recovered from a hamstring injury, looked threatening from set-piece play.
But it was United who almost went in front as Stephen Quinn's inswinging corner from the right after 10 minutes saw Beattie head over at the near post.
Preston lost the services of Liam Chilvers inside 20 minutes when the defender was forced to withdraw from the action, but their fortunes improved thereafter.
Carter flashed a left-foot shot from 12 yards high and wide from Karl Hawley's lay off.
Beattie then headed over from 12 yards following debutant Phil Bardsley's right-wing cross before North End took the lead.
Carter, who played under United manager Bryan Robson at West Bromwich Albion, played a straightforward inswinging ball into the hosts' penalty area from the right wing nine minutes before the interval.
The Blades failed to clear and the ball bounced twice before eluding Youl Mawene and Karl Hawley and creeping inside Paddy Kenny's far post.
Jonathan Stead and Stephen Quinn were replaced at half-time by Luton Shelton and Webber as Robson introduced pace to his attack.
Two minutes into the half, Webber came inside off the left wing, played a one-two with Shelton before laying the ball off for Alan Quinn, whose shot from the edge of the box was deflected for a corner.
Bardsley, signed on a three-month loan from Manchester United during the international break, went close with a crisp long-range drive after 62 minutes.
His half-volley dipped and forced Andrew Lonergan to save at full stretch.
It provided a spark for United and Alan Quinn shot straight at Lonergan moments later.
The route one approach continued, with the Blades relying on Kenny's long clearances up field.
Webber latched on to one after 78 minutes and ran at St Ledger, with the ball bouncing up and making contact with his arm.
Mr Singh pointed to the spot and Beattie duly converted, with Preston boss Paul Simpson sent to the stands for voicing his displeasure.
Lonergan denied Shelton from close range as United looked the more likely to grab a winner but Preston held on in a tense finale.