Kildare finished strongly at O'Connor Park to knock out the defending champions.
Offaly's quest to retain the Leinster and All-Ireland Under 20 Football Championships has been halted.
A goal for Kildare's Jack Quinn with ten minutes to go gave the Lilywhites a lead they wouldn't relinquish in last night's Leinster semi-final at O'Connor Park.
It finished 2-11 to 0-15 in Tullamore, and Kildare will go on to face Dublin in the Leinster final after they beat Meath 4-12 to 1-14 at Parnell Park.