Arsene Wenger's side cemented their fourth-place finish with a composed victory against the Magpies, with the match-winning goal coming from their French centre-back
The Gunners' victory meant that regardless of how Tottenham got on against Sunderland at White Hart Lane, they would be the north London side appearing in the Champions League come September.
Arsene Wenger risked Mikel Arteta from the start after the Spain midfielder was given injections in his calf on Friday to patch up the injury he sustained in the midweek win over Wigan, but the decision proved a poor one as the Gunners captain was forced off through injury in the 29th minute.
Newcastle marked Steve Harper's final game by handing him the captaincy for the day, as the goalkeeper reached the end of a 20-year spell at the club. The 38-year-old was afforded a marvellous send-off by Newcastle's supporters as they chanted his name for the duration of the 37th minute, to symobolise the goalkeeper's shirt number.
Newcastle barely touched the ball in the opening five minutes as Santi Cazorla and Aaron Ramsey dominated possession in midfield for the visitors, and that impressive spell was only broken by a thunderous challenge from Cheick Tiote on Tomas Rosicky.
The hosts fashioned the first chance of the game in the 10th minute when Papiss Cisse fired just over after strong play down the left-hand side from Mapou Yanga-Mbiwa.
Alan Pardew's side continued to threaten down the flanks, as Hatem Ben Arfa and Yoan Gouffran enjoyed themselves playing in an attacking three off Cisse.
Wenger's decision to start Arteta despite the calf injury he picked up against Wigan during the week backfired shortly before the half hour mark, as the former Everton midfielder had to be replaced by Alex Oxlade-Chamberlain.
Arsenal appeared to click through a couple of gears at the start of the second half, as Theo Walcott and Cazorla began to run at Newcastle's defence, and in the 52nd minute their pressure told when Koscielny gave them the lead. The Frenchman was on hand to smash a close range volley past Harper after Theo Walcott's free kick sat up for him inside the Newcastle penalty area.
Just moments after going ahead the Gunners were fortunate not to concede a free kick in a very dangerous position, as the ball struck Ramsey's arm as he slid to dispossess Ben Arfa in full flight. Despite being just yards away from the action Howard Webb waved play on.
Newcastle withdrew Yohan Cabaye shortly after, and that sapped the life from the hosts' play as Arsenal bookended their performance by dominating possession in a similar vein to how they started the game and defended resolutely to claim three massive points.