A great goal from veteran John Shaw ten minutes into the second half proved crucial as Raharney cruised into the provincial semi-final.
The wind-assisted Westmeath champions started in blistering fashion with the 17-year-old Doyle twins, Ciaran and Killian, contributing an unanswered 1-3 between them to open up a six-point lead with less than six minutes elapsed.
The goal came from a long-range free from near the sideline by Killian, the ball going in off a defender's hurley.
The same player had a great chance to score a second goal in the seventh minute, but his weak shot was saved by Kevin Kehoe.
With Marty Kavanagh in fine form from frees despite facing into the wind, the Carlow men clawed their way back into contention.
However, Kavanagh lacked support and Raharney continued to dominate in most sectors, but they missed a number of opportunities, with Killian Doyle shooting five wides from scoreable placed balls, and the deficit was down to four points at the break (1-5 to 0-4).
With the strong wind now in their favour, three more points from Kavanagh (two from frees and a great score from play) left St Mullins just a point in arrears after 36 minutes.
However, a point from Robbie Greville (following a quick-thinking quick free by Ciaran Doyle) and Shaw's goal turned the tie firmly in favour of the home team who looked likely winners from that moment on.
The goal was taken skilfully by the Christy Ring Cup-winning captain from 2005 (right) as the corner-forward was stumbling to the ground when fouled, having received the ball from Brian Smyth's probing delivery.
The Doyles added three more points between them for Raharney, while Kavanagh and wing-back Paudie Kehoe both converted frees for the Carlow men.
Sandwiched between two late frees from Raharney substitute Brian Connaughton, St Mullins full-forward Seamus Murphy picked up a straight red card in the 59th minute of what had been an incident-free and sporting contest.
Andrew Doyle pulled off a great save from Paudie Kehoe in injury-time as St Mullins went all out in search of a goal, but Raharney's win had not been in doubt from a long way out.
The Westmeath outfit now face former All-Ireland finalists Kilcormac/Killoughey from Offaly, in the provincial semi-final, also in Mullingar, on Sunday week.
Scorers: Raharney: K Doyle 1-4 (1-4fs), J Shaw 1-0, C Doyle 0-3, B Connaughton 0-2 (2fs), C Boyle, R Greville 0-1 each. St Mullins: M Kavanagh 0-8 (6fs), P Kehoe 0-1f.
Raharney: A Doyle; T Doyle, C Jordan, D Giles; G Greville, P Greville, A Sheils; N Flanagan, C Boyle; J Boyle, K Doyle, R Greville; C Doyle, B Smyth, J Shaw. Subs: C Flanagan for J Boyle (38), B Connaughton for N Flanagan (54).
St Mullins: K Kehoe; P Doyle, J Doran, D Whelan; P Kehoe, G Coady, P Fortune; M Walsh, C Kavanagh; M Kavanagh, J Murphy, T Doyle; J Doyle, S Murphy, J Kavanagh. Subs: D Murphy for Fortune (h-t), J Walsh for M Walsh (53).
Referee: G McGrath (Dublin).