The success, this second provincial U21 title in three years, sets up an All-Ireland semi-final against either Cavan or Tyrone in a fortnight.
Sligo won the toss but their decision to play against the breeze backfired spectacularly.
Finbarr Cregg and Brian Egan swapped early frees but Roscommon took charge despite playing second fiddle at midfield. Captain Paddy Brogan and Niall Kilroy typified Roscommon’s workrate as Sligo turned over possession far too easily.
Five points from Smith, including four frees, alongside scores from Cian Connolly, Conor Daly and a fisted effort from Scott Oates pushed Nigel Dineen’s side 0-9 to 0-1 ahead. Pat Hughes stopped the rot for Sligo on the stoke of half-time but his side still trailed by seven points at the break.
The impressive Colin Compton pointed for Roscommon inside a minute of the new half. Three points in succession, two from Egan and one from midfielder David Maye, hinted at a Sligo revival. But a free from Smith was soon followed by an emphatically converted spot kick from the same player as Roscommon eased to victory.
ROSCOMMON: T Lowe; C Cafferky, C Duignan, D Murray; C Daly (0-1), P Brogan, R Stack; F Kelly, N Daly; S Oates (0-2), N Kilroy, F Cregg (0-1, 1f); C Connolly (0-1), C Compton (0-2), D Smith (1-6, 5f, 1-0 from penalty).
Subs: C Shine for Cregg (49), J McManus for Kelly (53), C Murtagh for Connolly (58), A Feehily for Oates (60).
SLIGO: V Cadden; J Kelly, D Carobine, P Laffey; C Moloney, M O’Hehir, L O’Connell; D Maye (0-1), J Clarke; C Brennan, P Hughes (0-1), E Kivlehan; B Egan (0-3, 2f, 1 ‘45), N Murphy (0-2, 1f), C Brennan.
Subs: D Coffey for Carobine (17), C O’Dowd for Moloney (36), J Rodgers (0-1) for Kivlehan (48), C Killoran for Brennan (54).
Referee: R McBrien (Leitrim).