Ulster had went into the half-time break with a 10-0 lead, after Joel Barron's finish in the corner and Daniel Green's drop goal in the first half.
Ricky Andrew's side got the first try of the second half to surge into a 17-0 lead, but the Westerners rallied well and hit back with three tries in the second period to make it a nervy ending for an Ulster side who did well to see the game out.
The opening 15 minutes of the game saw both sides attack and both defences looking solid and organised.
Connacht spent a sustained period in the Ulster 22, but the home team looked solid and forced the turnover of possession.
A super kick from the superb fly-half, Daniel Green, forced Connacht into a lineout on their 22m line. Ulster were able to pile on the pressure and turnover, leading to a dangerous attack.
Playing it wide, the backs worked the ball well and sent Joel Barron into space on the left.
The winger pinned his ears back and stretched for the line, scoring a wonderful opening try of the contest.
Daniel Green’s conversion from the left angle was struck powerfully and was on the money for a 7-0 lead.
Connacht were aiming to put Ulster's backline under pressure with spiral balls and trying to use their kicking game throughout the half.
Big lock, Ryan Halpin, made a crucial intervention at one point, doing well to gather a high ball that bounced in a dangerous area.
Ulster played patient rugby and ventured into the Connacht 22, aiming for their second try of the half.
With Connacht's defence staying stubborn and keeping Ulster at bay, Daniel Green strayed into space, demanding the ball.
The ten expertly slotted away a drop goal, taking the three points to send Ulster into a 10-0 lead at the interval.
HT: Ulster U19 20-19 Connacht U19
Ulster began the second half strongly and extended their lead. The home side had themselves a lineout opportunity in the Connacht 22 after a superb turnover from loosehead prop, Tyrese Abolarin, who was tenacious and commanding all game.
Skipper, James Clark, got the finishing touch after Ulster's lineout maul powered towards the Connacht tryline. Daniel Green's kick was struck well and Ulster now led 17-0.
Connacht would rally with two lineout maul tries of their own through Jack Pollard and Oisin McNicholas, with one conversion.
The away side were feeling the momentum. Ulster gave themselves a but of breathing room after Daniel Green nailed a penalty in the Munster 22 to make it 20-12.
Connacht kept going and notched their third try, after a Thomas Cotton broke through the line and passed to his supporting runner, Charlie O'Carroll, who slid through for the score. Elwood’s conversion narrowed the scoreline to a one point game.
Ulster got their heads down and put up a dogged fight, with massive turnovers from Tyrese Abolarin and Josh Dobbin, just as Connacht looked to break Ulster hearts at the death.
Scott Gray was given a red card late on for a deliberate knock on and a double yellow offence but Ulster managed the closing seconds well and Green ended the contest by kicking it into the stands.
Ulster players were overjoyed at the victory that was full of grit and determination, as they secured their interpro victory in front of a home crowd in Belfast.
FT: Ulster U19 20-19 Connacht U19
Player of the Match - Tyrese Abolarin
Made some vital turnovers during the game and was a real threat at driving the ball forward and putting Connacht under pressure. Work-rate was fantastic from the talented prop, who plays his school rugby for Methodist College Belfast.
Scorers
Ulster:
TRY: Barron, Clark
CON: Green x2
PEN: Green
Drop Goal: Green
Connacht:
TRY: Pollard, McNicholas, O’Carroll,
CON: Elwood x2
Teams
Ulster
(1-8) Tyrese Abolarin (MCB), James Clark (C)(RBAI), Rio McDonagh (Wallace HS), Ryan Halpin (Down HS), Scott Gray (CCB), Jake Scott (Sullivan Upper), Matthew Heasley (Dromore HS), Callum McKinney (CCB)
(15-9) Evan McGonigle (Regent House), Henry Ralston (CCB), Quinn Armstrong (Wallace HS), Rob Henderson (Friends'), Joel Barron (Friends'), Daniel Green (IQ), Callum Soper (RBAI)
Replacements: Aaron Caldwell (BRA), Zak Molyneaux (RBAI), Josh Dobbin (Cambridge House), Ethan Pavlovic (BRA), Ryan Hanna (Banbridge Academy), Lewis Stevenson (Wallace HS), Charlie Gray (RBAI), Ethan Spratt (Regent House), Hayden Hamilton (Regent House)
Connacht U19
15\. Paul Sharkey (Galwegians RFC / St. Joseph's Patrician College)<br>
14. Ronan O'Connor (Sligo RFC / Summerhill College)<br>
13. Thomas Cotton (Buccaneers RFC / Marist College)<br>
12. Tom Sheehan (Buccaneers RFC / Marist College)<br>
11. Dylan Bruton (Buccaneers RFC / CBS Roscommon)<br>
10. Calum Elwood (Galwegians RFC / Coláiste Iognáid)<br>
9. Billy Ruane (Ballina RFC / St. Muredach's College)<br>
1. Rory Lyons (Westport RFC / Sancta Maria College)<br>
2. Jack Pollard (Buccaneers RFC / Garbally College)<br>
3. Brian Donohoe (Ballina RFC / St. Muredach's College)<br>
4. Liam Cahill (Corinthians RFC / Coláiste na Coiribe)<br>
5. Leo Anic (Creggs RFC / CBS Roscommon)<br>
6. Pasha Thiam (Corinthians RFC / Coláiste Éinde)<br>
7. Charlie Keane (Corinthians RFC / Coláiste Bhaile Chláir)<br>
8. Oisin McNicholas (Ballina RFC / St. Louis Community School)
16\. Eoin Naughton (Buccaneers RFC / Cistercian College Roscrea)<br>
17. Michael Donnelly (Castlebar RFC / St. Gerald's College)<br>
18. Jason Duggan (Ballina RFC / St. Muredach's College)<br>
19. Michael Smyth (Claremorris RFC / St. Louis Community School)<br>
20. Donagh Kilcommins (Corinthians RFC / Coláiste Bhaile Chláir)<br>
21. Charlie O'Carroll (Buccaneers RFC / Marist College)<br>
22. Joseph Smyth (Ballinasloe RFC / Garbally College)<br>
23. Mark Tempany (Sligo RFC / Sligo Grammar)