Fred Onyedinma scored twice as Wycombe held off a spirited Fleetwood featuring Glenn Whelan to reach the Sky Bet League One play-off final following a 2-2 draw at Adams Park.
The Chairboys had taken control of the first leg, easing to an emphatic 4-1 victory at Highbury against nine men, and did enough to book their place at Wembley with a 6-3 aggregate success.
Fleetwood took the lead in the 22nd minute after an early period of pressure. The Wycombe defence cleared the ball straight into the path of Danny Andrew and he fired home to offer Joey Barton's side hope of a stirring comeback.
But Wycombe hit back just after the restart, with Onyedinma capitalising on a defensive mistake to level on the night and put his side firmly back in control.
The visitors regained the lead through Ched Evans' second penalty of the tie, only for Onyedinma to grab his second goal of the game at the death to seal his side's passage.
Ireland international midfielder Whelan played the full 90 minutes while Paddy Madden was suspended having been sent off in the first leg on Friday.
Wycombe will face Oxford in the final on 13 July as they attempt to reach the second tier of English football for the first time in their history.
Limerick native Anthony Forde came on in extra-time and scored in the shootout as as Oxford beat Ireland international Ronan Curtis' Portsmouth 5-4 on penalties at the Kassam Stadium.
Having drawn 1-1 at Fratton Park on Friday, the sides played out the same scoreline on Monday evening as Ellis Harrison's own goal cancelled out Marcus Harness' opener for the visitors.
Cameron McGeehan missed Pompey's fourth spot-kick as Kenny Jackett's side crashed out at this stage for the second year running.
Former Ireland U21 Liam Kelly was an unused sub for the winners.