The 28-year-old striker was dismissed for an innocuous-looking 50-50 challenge with former Villa team-mate Ashley Young in the 65th minute of last Saturday's 1-1 draw at Villa Park.
He appeared to make minimal contact with Young's shin, but referee Lee Mason deemed the challenge worthy of a red card.
The FA announced on Tuesday that they had reversed the decision, meaning Agbonlahor is free to face Swansea City on December 26.
Villa have, though, been charged with "failing to ensure that its players conducted themselves in an orderly fashion" in reacting to the decision.
An FA statement read: "Gabriel Agbonlahor will be available for Aston Villa's Boxing Day fixture with Swansea after an FA Regulatory Commission upheld his claim of wrongful dismissal.
"Agbonlahor was sent off for serious foul play in his side's 1-1 draw with Manchester United on Saturday 20 December 2014.
"Meanwhile, Aston Villa have been charged with failing to ensure that its players conducted themselves in an orderly fashion in or around the 65th minute in the same fixture.
"The club has until 6pm on 30 December 2014 to respond to the charge."
