Coláiste Iognáid coach Stephen Parkinson was thrilled with his side's efforts as they made it back-to-back titles with a hard-fought victory over Summerhill College.
Last year the Jes won their 13th title when they beat Garbally College 16-15 in a thrilling decider, and this was another tight encounter, but the Jes were too strong.
Tighthead prop Gary Keane touched down the crucial try before half-time, while Diarmuid Codyre added a conversion and two penalties.
Caoileann Carty scored a late consolatory try for Summerhill but it wasn't to be, and their wait for a first-ever Connacht Senior Cup title goes on.
"We made heavy weather of it for a while. We were dominant but we just weren't putting them away," said Parkinson.
"I'm glad for Summerhill's sake they got a score before the end because it showed the work that they put in. But we were calm and I'm glad we got over the line."
After Ross Hickey was sin-binned in the 26th minute Codyre tapped over the penalty, and The Jes held a 10-0 half-time lead after Keane's try.
But they had to wait until seven minutes before the end for their next score, before Summerhill grabbed a late try through Carty.
Coláiste Iognáid - A Cunningham; C Briscoe (R O'Flynn 58), T Forde, C McCabe (G Kenny 46), D Molloy; D Codyre, E Kenny (R Durkin 55); A Corbett, C Fallon, G Keane (S Monaghan 45); D O'Connor (T Power 55), A Mannion (C Parsons 30); J Gallagher (M Higgins 58), C McGuinness (C Anthony 54), H Keaveney.
Summerhill College - H Kisby; C Murray (T O'Hehir 36), K Connell, R Hickey, R Solano; B Cox, B Cunningham; M Keegan, V Reynolds, C McGovern; C Carty, G Golden; F Doherty (Y Shalabi 30), S Wynne, A Cummins.
Ref - Jason Cairns.