RYAN McMANUS bagged the only goal of the game to secure Summerhill College their first national crown since 1997.
The midfielder, who later missed a penalty, put CBS Sexton Street on the back foot at Home Farm FC in Whitehall after 15 minutes by supplying an exquisite finish.
When Eoin Nicholson's shot was blocked, McManus controlled the rebound on the edge of the box and with goalkeeper Jamie Stewart out of his goal, the match winner remained composed to finish into an empty net.
McManus should have had his second on the half-hour from the penalty spot, but Stewart in the CBS goal got down well to save.
The Limerick school were given another let-off on the stroke of half-time as Jack Selby's header crashed back off the crossbar, but they improved for the second half.
For all their territorial dominance, however, the All-Ireland champions of 2008 and 2009 lacked a clinical edge in the final third and their challenge fell short.
Meanwhile, Waterford's De La Salle lifted the Junior Boys national title in Balbriggan by defeating Scoil Mhuire, Buncrana 2-0 thanks to Maurice Shanahan's brace.
SUMMERHILL COLLEGE – R Blake; B Glennon, J Selby, J Dykes, S Kerins; D Kilcawley, R McManus, M Casey (D Smith 84), E Nicholson; G Armstrong, C Feeney.
CBS SEXTON – J Stewart; A Moran, S Mullins, G O'Connor (C Madden 85), L Whyte; T Hogan, J Mullins, S Walsh, C Hogan; J Bromell, E Byrnes (N O'Connor 85).
REF – E Reilly.