Saracens will take on Northampton Saints on May 31 after beating Harlequins 31-17 at Allianz Park this afternoon.
Mark McCall's side overcame a half-time deficit to progress to their first Premiership final since lifting the title at the expense of Leicester Tigers in 2011.
Brad Barritt and Chris Ashton scored after the break to send Sarries to Twickenham.
The Men in Black had temporarily been down to 13 men after Marcelo Bosch and Matt Stevens were sin binned in the first-half.
Ugo Monye took full advantage of Sarries' ill-discipline to put Quins ahead before Kelly Brown levelled for Saracens.
Mike Brown put the visitors back in front before Barritt scored Saracens' second try.
Ashton's try secured Saracens' progression to the final, with Owen Farrell kicking two conversions and four penalties for McCall's men.