Wycombe now look like missing out on the play-offs after stretching their winless run to eight games.
Hartlepool bossed most of the first half through a mixture of neat football and hard work but it was Wycombe who created the first real chance after 15 minutes.
Tommy Doherty played in Tommy Mooney who then squared for Scott McGleish, but the oncoming keeper forced him wide and he just ran the ball out of play.
The visitors hit back well and had the best chance of the half some five minutes later. A long throw fell nicely to Andy Monkhouse whose improvised volley hit the post.
Hartlepool continued to dominate but did not create much in the way of chances for the rest of the half.
Wycombe manager Paul Lambert must have had some strong words with his players in the break as the hosts stormed out of the blocks in the second-half creating two very decent chances.
Firstly, Mooney played in Jermaine Easter who went one-on-one with keeper Dimitrios Konstantopoulos but the striker panicked and prodded his shot wide.
Then Easter was provided with another great chance. After a slick passing move the Welshman was put through again but this time he shot straight at Konstantopoulos.
Seconds later Hartlepool went down the other end of the pitch and had a glorious chance. A blocked shot fell kindly to Gary Liddle but his shot was well saved by Ricardo Jorge Batista.
The visitors then had two great chances to win the game. Substitute Joel Porter wasted the first, firing straight at Batista. Then another substitute David Foley was well denied by the keeper when he followed up a good save following an effort from Liddle.
Hartlepool finally scored the goal which sealed their promotion. With 10 minutes left, top-scorer Barker headed home from five yards after a precise cross from Monkhouse.