The winner will take on either Moate CC or Ardscoil na Tríonóide of Kildare.
Coláiste Mhuire Mullingar are currently gearing up for their Br Bosco Cup Senior Leinster semi final against Maynooth Education later today.
The Westmeath School will be looking to pick up where they left off after a 2-11 to 1-05 win over Dublin school Colaiste Eoin in the quarter final.
Their Kildare opponents reached this stage by beating Colaiste Choilm of Tullamore in a low scoring affair.
The contest will throw in at the Killucan GAA club in Westmeath at 12:30.