Palace beat Aston Villa 3-0 at Wembley Stadium on Saturday to advance to the May 17 title match back at the home of English soccer.
It will be the south London club's third appearance in the final, after 1990 and 2016. On both occasions, Palace were beaten by United.
Eberechi Eze smashed home a shot from the edge of the area in the 31st minute for the opening goal after good work from Ismaila Sa, who then finished Villa off with two second-half goals.
Sa scored in the 58th and again in the fourth minute of stoppage time to seal a convincing win over opponents who had reached the Champions League quarter-finals this season.
Villa, seven-times FA Cup winners, were eliminated from Europe by Paris Saint-Germain last week and now have just a top-five finish in the Premier League to play for as they look to secure a return to the Champions League. They currently lie seventh in the league.
It could have been a bigger margin of victory for Palace, with Jean-Philippe Mateta missing a penalty in the 53rd.
Palace, who've never won a major trophy, will meet either Manchester City or Nottingham Forest in the final. They meet on Sunday, also at Wembley.
16°C