Boro 3 (Tomlin 54, 90+3, Graham 90)
Reds 1 (M'voto 53)
Barnsley will be playing football in the third division next season - confirmed after defeat at Middlesbrough's Riverside Stadium.
Very little goal-mouth action occured in the opening 12 minutes, with Steele having to clear a stray pass which Reach couldn't catch early on.
There was a half chance as Pedersen's shot deflected off O'Grady but it didn't quite catch Konstantopoulos out on 11 minutes after Jennings had turned in the cross from the left.
Boro broke with Graham on 18 minutes and managed to get the ball from under his feet and unleash a shot that sailed over the bar from 20 yards.
With very little happening and both sides spending time on the ball in the middle third, Tomlin had the next strike but Steele got down well to his right on 30 minutes.
Barely a minute later Tomlin forced Steele into another save which rebounded to reach and his shot flashed across the face of goal with Adomah lurking. It was a lucky escape for the Reds.
Adomah then twisted and turned after Cranie had blocked Graham's shot into his path but Steele again denied the effort low to his right on 33 minutes.
The Reds were living life dangerously as Adomah again went close from inside the area on 39 minutes but Cranie blocked away. Butterfield then forced Steele into yet another stop - his best so far - with a vicious drive from 25 yards.
It looked inevitable that Boro would break the deadlock and once more Steele had to deny Reach from the edge of the area three minutes before the break.
Barnsley simply weren't learning from their mistakes and were all over the shop. Tomlin had acres of space to pick his spot but Steele again turned the ball away from his left for a corner.
Butterfield picked a pass out that split the Reds' defence open as it turned into a chance per minute for the hosts towards the end of the half. But, thankfully, Steele was quick off his line to smother Gibson with a smart tackle.
The Reds needed to find something in the second half if they were to have a chance of survival.
O'Grady saw a shot on the turn deflect off Ayala and over as the following Tykes cheered on from the corner.
From absolutely nowhere the Reds found the net and it was Jean-Yves M'voto on 53 minutes. A corner from the far side was met by the big Frenchman on the volley with his left peg and somehow it found the corner.
And after opening the scoring, M'voto gave the ball away for Boro to equalise within a minute. Tomlin picked up the ball from M'voto on the edge of the box and stroked home into the corner.
Luke Steele was back in action to make another flying save from Graham's wicked free-kick 30 yards out.
The Reds made a double change on the hour with Jim O'Brien back from injury replacing Lawrence and Nick Proschwitz coming on for Marcus Pedersen.
Dawson went on a great run down the right on 66 minutes to find Proschwitz and he shot from distance which Konstantopulos did well to handle.
The German had a better chance two minutes later when M'voto pass dropped into his path but his left foot shot went a couple of yards wide.
Kennedy put in a great out-swinging corner on 74 minutes which M'voto met unmarked with his head but couldn't direct it under the bar.
The Reds were alive now but it was crunch time. Jim O'Brien drilled in a cross after Proschwitz found him on the right but Boro cleared on 78.
Barnsley's final throw of the dice saw Danny Rose come on for Ryan McClaughlin with nine minutes left.
With Barnsley open at the back, Steele had to deny Boro a winner when Tomlin was found by Chalobah but his shot was saved.
Boro's winner came in the 90th minute as Barnsley were exposed at the back. Chalobah bombed forward, Adomah's shot was saved but Graham thumped in the rebound.
Five minutes was added but Barnsley were relegated. It was rubbed in their faces as Boro added a third through Tomlin.
Boro: Konstantopoulos, Omeruo (Hines 67), Varga, Butterfield (Chalobah 60), Reach, Tomlin, Graham, Woodgate (Ayala 41), Whitehead, Adomah, Gibson.
Subs: Steele, Maine, Ledesma, Morris.
Reds: Steele, McLaughlin (Rose 81), Kennedy, M'voto, Cranie, Etuhu, Dawson, Lawrence (O'Brien 60), Jennings, O'Grady, Pedersen (Proschwitz 60).
Subs: Turner, Cywka, Mellis, Ramage.
Attendance: 14867 (751 Reds)