The 2009-10 Celtic League Grand Final was the final match of the 2009–10 Celtic League season. The 2009-10 season was the fourth sponsored by Magners and was the first ever Celtic League Grand Final. The final was won by the Ospreys who defeated Leinster by 17-12 at the RDS Arena to win their third Celtic League title, the win ended Leinster's 20-month unbeaten home league record.

First half tries from Tommy Bowe after twenty minutes and Lee Byrne after thirty five minutes which were both converted put the Ospreys 3-14 up at half time, with the Leinster score coming from a Jonathan Sexton penalty after twenty three minutes. A further penalty from Sexton brought the score to 6-14 before Dan Biggar kicked over a penalty for the Ospreys after forty eight minutes. Two more penalties from Sexton in the sixty second and seventy first minutes made the score 12-17, but that was enough for the Ospreys to hold and become the first side to win the title for the third time.

Ospreys head coach Sean Holley reacted to the win saying "it's a special night, I wouldn't say it was our best performance, but certainly one of our most courageous and determined." "Leinster are pretty outstanding in defence, and it's the end of a long, hard season, I'm not that surprised (we cut through them), because we have some great talent." Departing Leinster coach Michael Cheika reacted to the loss by saying "Ospreys deserved the win but we're disappointed with ourselves. We didn't play well, we tried to fight our way back into the game, but we made too many mistakes. We probably just weren't accurate in the defensive section or where we needed to be in the team."

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