كتب : Hatem Maher
Midfielder Glenn Whelan put Ireland ahead after eight minutes but Italy winger Mauro Camoranesi leveled the score on 26 minutes.
St Ledger looked to have given Ireland all three points when he struck with three minutes remaining but substitute Gilardino, who came off the bench in the 76th minute, secured a share of spoils in stoppage time.
Italy ensured they would finish on top of Group Eight regardless of the outcome of their last game against Cyprus.
They lead second-placed Ireland by four points as the latter will play-off against another runner-up for a spot in next year's South Africa finals.
France will also play in the play-offs after a brace from striker Andre-Pierre Gignac and goals from William Gallas, Nicolas Anelka and Karim Benzema gave them an easy win over Faroe Islands.
They are four points behind Group Seven leaders Serbia, who qualified for the World Cup after thumping Romania 5-0.