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A dominant performance from the pack enabled England to hit back after Alison Miller gave Ireland a 7-0 lead.
Tries from Rochelle Clark, Kat Merchant, Kay Wilson and Marlie Packer (two) secured victory.
England, who lost the three previous finals to New Zealand, will play Canada, with whom they drew 13-13 in the pool stage, in the final.
Canada withstood late pressure to beat hosts France 18-16 in the other semi-final.
Ireland were out-gunned by England's all-round superiority, led by a bruising scrummaging performance.
However, after a previous best finish of seventh in a World Cup, they will look back with satisfaction at reaching the semi-finals for the first time.
Their pool win over New Zealand - the defending champions - was the biggest shock in the history of the competition, but it is possible it left them too drained to once again hit the same heights in order to see off England at Stade Jean-Bouin.
For the first 20 minutes the Irish were on top and they took the lead as winger Miller found herself at the bottom of the heap after Ireland's pack had driven a maul over from a line-out.
Full-back Niamh Briggs, who had an outstanding tournament, landed the tricky conversion to make it 7-0 with 15 minutes played, and England were looking rattled as the Irish disrupted their line-out and used the choke tackle to force a steady stream of turnovers.
England finally opened their account with a similar score to Ireland's as prop Clark burrowed over after a driving maul, and the Red Roses assumed control in the final 10 minutes of the half.
Emily Scarratt was at the heart of the action, a couple of damaging runs opening up the Irish defence and a couple of accurate penalty kicks atoning for her earlier missed conversion.
In between the outside centre's two penalties, she also converted England's second try after her 50m break set up the position for winger Merchant to finish in style.
England were suddenly in total control and Ireland, 18-7 down at the break, needed to start the second half strongly if they were to reach a maiden final.
Instead it was all England after the restart and, with their pack increasingly dominant in the scrum, the Red Roses first battered the Irish into submission up front and then exploited the space out wide to romp away.
Scarratt extended the lead with her third penalty and Wilson added a third try just before the hour mark.
England took off a number of players to rest them for the final, including captain and fly-half Katy Mclean, and replacement flanker Packer seized her chance to score a rapid brace of tries, both converted by replacement 10 Ceri Large.
England: Waterman; Merchant, Scarratt, Burford, Wilson; Mclean (capt), Mason; Clark, Fleetwood, Hemming, Taylor, McGilchrist, Matthews, Alphonsi, Hunter.
Replacements: Croker (for Fleetwood, 63 mins), Essex (for Clark, 63, Clark for Hemming, 69), Allan (for Scarratt, 68), Keates (for Taylor, 63), Large (for McLean, 68), Packer (for Alphonsi, 63), Hunt (for Mason, 58).
Ireland: Briggs; Baxter, Cantwell, Davitt, Miller; Stapleton, Rosser; Coghlan (capt), Bourke, Egan; Spence, Reilly, Fitzpatrick, Molloy, O'Brien.
Replacements: Lynch (for Egan, 65), Murphy (for Davitt, 47), Hayes, Fleming (for O'Brien, 47), Guest (for Spence, 72), Muldoon (for Rosser, 66), Casey (for Cantwell, 68).
England reached the Women's Rugby World Cup final for the fourth time in a row as they outclassed Ireland in Paris.