Though fighting to stay up in the Premier League, Villa was superior for most of the game at Wembley Stadium against a team that still has slim aspirations of qualifying for the Champions League.
Yet, it was Liverpool that took the lead in the 30th minute following a lacklustre opening to the game,
Following a deft pass from Raheem Sterling, Philippe Coutinho poked the ball past diving Aston Villa goalkeeper Shay Given from close range.
Villa responded well to going behind with Jack Grealish impressive on the left flank. In-form striker Christian Benteke put Villa level in the 36th minute after an incisive cutback from captain Fabian Delph. Benteke met Delph's pass with a low first-time strike that went past outstretching Liverpool goalkeeper Simon Mignolet, who managed to get his fingertips to the shot.
Liverpool manager Brendan Rodgers responded to Villa's growing superiority toward the end of the first half by bringing on striker Mario Balotelli for midfielder Lazar Markovic. But the substitution did little to alter the game and Villa started the second half in the same attacking vein it had ended the first.
Following a sustained period of pressure, Villa took the lead in the 54th minute when Delph started and finished a swift move that involved smart passes from Benteke and Grealish. Put through on goal by Grealish, Delph cut past Liverpool defender Dejan Lovren and then fired in the winner past Mignolet from 10 yards.
Liverpool struggled to impose itself on the game but did come close twice to forcing extra time. A header from Steven Gerrard was cleared off the line by Kieran Richardson in the 86th minute. Two minutes later, a goal from Mario Balotelli was ruled offside, although replays suggested he was well on.
Aston Villa will meet defending champion Arsenal, which beat Reading 2-1 Saturday in the other semifinal, on May 30.
The team from Birmingham has won the FA Cup on seven occasions but not since 1957. The last time it contested the final was in 2000 when it lost 1-0 to Chelsea.
Villa coach Tim Sherwood, who only joined the club in February after the sacking of Paul Lambert, conceded that his team will be "the underdog" at the final against what he considers to be the "best footballing side in the league."
The priority now, said Sherwood, is to ensure Premier League survival. Villa lies in 15th place and is four points above the relegation zone with five games to go.
"We need to secure our safety and then come back here and take the game to Arsenal," he said.
For Liverpool, defeat at the semifinal stage for the second time this season — the team also lost to Chelsea in the League Cup — means it has now gone three seasons without any silverware.
Though acknowledging that Liverpool was denied a legitimate goal, Rodgers said his team just wasn't good enough and appeared to be fazed by the occasion.
"I felt we were too passive," Rodgers said. "We've come up short in a few games. It's something we need to improve."
Defeat also means that captain Steven Gerrard won't end his 16-year Liverpool career with another trophy. Gerrard is leaving Liverpool at the end of this season to join the Los Angeles Galaxy.