The 34-year-old rose highest to nod in a Coutinho corner on 87 minutes to mark his penultimate game at Anfield with a winning goal after seeing his spot-kick saved
Gerrard rose highest to nod in a Coutinho corner on 87 minutes soon after seeing a penalty saved by Robert Green as he marked his penultimate match at Anfield with a winning goal.
Leroy Fer had earlier bundled in a corner to cancel out Coutinho's beautifully-worked first-half opener and give QPR hope in their increasingly forlorn battle against relegation, but Gerrard had the final word.
Nedum Onuoha collected a second booking for a rash foul on substitute Jordon Ibe and QPR were unable to hang on as the Liverpool captain planted a header past Green.
The defeat means QPR are seven points from safety with three games remaining and Chris Ramsey's men could be relegated by the time they take to the field at Manchester City next Sunday.
Liverpool edge nearer to a Europa League spot and manager Brendan Rodgers will have enjoyed Gerrard stealing the headlines from a plane that flew over Anfield before kick-off, sporting a banner calling for him to be replaced by former boss Rafael Benitez.
Gerrard returned for Liverpool alongside Adam Lallana and Rickie Lambert, as both teams wore black armbands as a mark of respect following the passing of QPR defender Rio Ferdinand's wife Rebecca Ellison.
Fer - starting ahead of Bobby Zamora in QPR's only change - had the ball in the net within the first minute, but the officials ruled that Matt Phillips' scuffed corner went out of play.
Phillips sent a more convincing delivery into the Liverpool box in the eighth minute, but Steven Caulker was unable to turn an acrobatic volley home.
Lambert was making a first Premier League start in attack since December and he capitalised on an error from Rangers captain Joey Barton to thud a 20-yard drive into the arms of Green.
The hosts had hit their stride by the time Lambert cut a ball across the area for Coutinho, who took a touch before stylishly finding the top corner.
An offside flag denied Raheem Sterling when he converted on the end of a deft backheel from Jordan Henderson in the 33rd minute.
QPR top scorer Charlie Austin blazed wide on the turn during an increasingly rare attack for Ramsey's men, while Green kept out a Gerrard free-kick.
Lallana wasted a glorious chance five minutes into the second half as Coutinho unpicked a flagging QPR defence - now without Caulker due to a suspected broken hand.
That miss was surpassed by England team-mate Sterling, who lifted over from close range four minutes later when found by a wonderful Henderson cross.
There was little let-up from the home side, with Green saving from Lambert and Dejan Lovren either side of a Gerrard strike being deflected wide by Clint Hill.
Liverpool rued their poor finishing when Fer was allowed ample room to volley home from Barton's right-wing set-piece.
Green's heroics and something far less desirable from Onuoha then set the stage for a Gerrard to send the Kop into familiar raptures.