The Saddlers, who have never been to Wembley in their history, edged through 2-0 on aggregate on Tuesday night after their first-leg win.
Tom Bradshaw had Walsall’s best chance in a scrappy game while Sylvan Ebanks-Blake hit the crossbar and Chris Humphrey was denied by Richard O’Donnell for underwhelming Preston.
The final whistle sparked a pitch invasion from the home fans and the Saddlers will face either Bristol City or Gillingham in March’s final.
Both sides made one change with Paul Downing replacing Ben Purkiss for the hosts while Kevin Davies came in for Ebanks-Blake up front for the visitors.
Jordan Cook fired well off target early on in a low-key opening as the Saddlers protected their first-leg advantage.
Tom Clarke header over after 20 minutes and Bradshaw, who scored in the first game at Deepdale, drilled wide as the sides traded half chances.
But Walsall were comfortable, not needing to pile forward, although they failed to conjure anything meaningful.
Their biggest concern was Kyel Reid’s threat as James O’Connor, who was wearing a headguard after having staples taken out of an injury, struggled to contain the winger.
While it remained goalless the Saddlers were in control but, true to boss Dean Smith’s pre-match pledge, they looked to kill Preston off.
Immediately after the break Anthony Forde’s shot deflected wide before Cook dragged off target in the opening three minutes of the second half.
And Romaine Sawyers missed a fine chance in the 50th minute when he failed to connect properly with Cook’s cross six yards out and Thorsten Stuckmann saved.
O’Donnell had been relatively untroubled but he was called into action when he spilled Paul Gallagher’s shot before saving Humphrey’s follow-up.
The game opened up and Walsall’s 15-goal top scorer Bradshaw planted a header over from eight yards with 25 minutes left.
And the Saddlers survived several scares in the dying minutes to book their place in the final.
O’Donnell saved Gallagher’s fierce free-kick before gathering Ebanks-Blake’s header with three minutes remaining.
In stoppage time, the keeper produced two fine blocks in a goalmouth scramble before the outstanding Downing cleared off the line.
Ebanks-Blake then hit the bar from distance but Walsall held on.