Billy Bodin's second goal of the season in the 40th minute appeared set to give Preston all three points at the City Ground.
But just two minutes after his 77th-minute introduction, midfielder Adomah – a free transfer capture from Aston Villa – slotted home an equaliser, just as he did 10 days ago after coming on as a substitute in a 1-1 draw at Charlton.
The first half was all Preston in terms of chances as Forest failed to record a shot on target, for while there was neat approach play on occasion from the hosts they were devoid of ideas in the final third.
Instead, it was the visitors who displayed the greater attacking intent, with Forest goalkeeper Brice Samba twice called into action around the 15-minute mark.
Initially, Josh Harrop played in Bodin who fired in a stinging left-foot shot that forced Samba into a fine save.
That was swiftly followed by Daniel Johnson unleashing a left-foot effort of his own from just outside the area that again tested Forest's French stopper.
Just as the half appeared to peter out to a goalless conclusion, Preston struck five minutes before the interval.
With Forest's defence unable to clear the ricochet, an effort from Alan Browne landed at the feet of Bodin, who made no mistake with his second attempt as he coolly slotted the ball past Samba.
Forest could easily have headed into the break 2-0 down as two minutes later Harrop was inches away from turning home a deep right-wing cross from skipper Paul Gallagher.
The introduction of Samba Sow at the start of the second half for Alfa Semedo at least provided Forest with an attacking spark, with the summer signing from Dinamo Moscow teeing up Lewis Grabban in the 52nd minute for an 18-yard right-foot curler that was just over the crossbar.
The arrivals of Joao Carvalho in the 68th minute and Adomah 10 minutes later were then the ultimate catalysts that ensured Forest are now unbeaten in their last seven matches.
It was Carvalho who played a superb through ball into Adomah, who tucked home his third goal in his past four appearances beyond the advancing Declan Rudd.
Forest then finished the stronger side, almost snatching an 87th-minute winner when a fast break culminated in Joe Lolley's rasping drive being palmed away by Rudd.