The Offaly club overcame Ellistown in Tullamore on Saturday.
Offaly's intermediate champions have booked their place in a Leinster final.
Ballinagar will face Dunsany of Meath in the provincial junior decider this weekend after they emerged from a testing encounter with Ellistown.
The Faithful County club found themselves four points to the good entering the closing stages of their semi-final before Ellistown mounted a resolved comeback to close the gap to a point.
Ballinagar were able to hold out from there to win on a final score line of 0-9 to 0-8.
They meet Dunsany in Pairc Tailteann for the Leinster Junior Football final at 1.30pm on Sunday.
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