Ayr United were relegated to Division Two and had two men sent off as Airdrie moved into the play-off final against Dumbarton after a win at Somerset Park.
Derek Holmes' second-half double and Willie McLaren's late strike secured a 3-1 victory on the day and on aggregate after Wednesday's goalless first leg.
Ayr got off to the worst possible start when midfielder Jackson Longridge was sent off for a two-footed lunge on Ricki Lamie after just 17 minutes.
Jonathan Tiffoney followed late on.
The 10 men made it to half-time without conceding but fell behind eight minutes after the break when they failed to clear Jamie Stevenson's corner, Kevin Cuthbert parried a shot from Jamie Bain and Holmes slotted in the rebound.
Ayr grabbed a surprise leveller just after the hour mark when Andrew Geggan guided in Eddie Malone's free-kick.
But, 60 seconds later, Holmes tucked away a cross from Ryan Donnelly and, with five minutes left, McLaren was left clean through on goal to seal the victory and a final clash with Dumbarton.
In stoppage time, 10 men became nine when Tiffoney collected his second yellow card to compound the misery for the side who finished second bottom of Division One.
Airdrie, who finished fourth in Division Two, will now take on Dumarton, who finished six points ahead in the league table and beat second-placed Arbroath 2-1 on aggregate.
Ayr: Cuthbert, Tiffoney, Martyn Campbell, Smith, Malone, Trouten, Geggan, McKernon (McGowan 78), Longridge, Moffat (Parker 60), Roberts. Subs Not Used: McWilliams, Ross Robertson, Hutchinson.
Booked: Roberts, Tiffoney, Parker. Sent Off: Longridge (17), Tiffoney (90).
Goals: Geggan 64.
Airdrie: Adam, McNeil, Stallard, Lilley, Lamie (Green 66), Bain, Lynch, Blockley, Stevenson, Donnelly (Boyle 86), Holmes, Green (McLaren 72). Subs Not Used: Duncan, Watt.
Booked: Blockley, Lamie, Green, Lynch, Stevenson.
Goals: Holmes 55, 65, McLaren 85.
Ref: Steven McLean