The midfielder rose unopposed to send a powerful header past Jonathan Brain after Nicky Nicolau's cross had found the former York man completely unmarked.
That goal capped a fierce fightback from Paul Fairclough's side after they found themselves two goals behind in the first seven minutes.
Two defensive howlers allowed Macclesfield a dream start as Jimmy McNulty and Levi Reid fired the visitors into a two-goal lead.
But Liam Hatch soon had Barnet back in business, his thumping header coming less than 60 seconds after Reid had doubled Macclesfield's advantage.
And when Bishop headed home a 90th minute equaliser, the comeback was complete as Fairclough's side avoided a third straight league defeat.
Having lost their last two home games 3-0, Barnet could not have envisaged a worse start as they gifted Macclesfield a two-goal lead within the first eight minutes.
Francis Green was fouled by Kenny Gillet and from the resulting free-kick, McNulty somehow managed to bundle the ball past four or five Barnet defenders, before smashing home past Lee Harrison.
Worse was to follow for the home side as another defensive blunder allowed Macclesfield to double their lead.
Harrison's misjudgement almost saw the goalkeeper slide out of his penalty area with the ball still within his grasp and after dropping the ball on the edge of his box - Reid took advantage of the situation - sidestepping the goalkeeper before slotting home into an empty net.
But Macclesfield's celebrations were short-lived as Barnet found themselves back in business less than a minute later, Hatch thundering home a header after Ashley Carew's corner had found the striker completely unmarked.
After a frenetic opening period, both teams seemed to settle down as much as they could in monsoon like conditions in North London.
Michael Leary's 30-yard piledriver flew inches over the Town bar, while Gareth Evans, on for the injured Martin Gritton, saw his speculative effort tipped away by Harrison.
The second half failed to spark into action until just after the hour mark as Green and Gillet came within inches of finding the target.
An off-the-ball incident then sparked a full 22-man ruck, with substitutes and Bees assistant manager Ian Hendon also finding themselves in the middle of proceedings.
Remarkably, referee Carl Boyeson, who gave a rather inconsistent display all afternoon, issued just three yellow cards when a couple of dismissals seemed inevitable.
With conditions deteriorating, neither side managed to create any real clear-cut chances, although Green should have done better from close-range after Danny Thomas' cross had picked out the former Lincoln man.
But with the clock ticking down, Barnet threw caution to the wind and came up trumps as Bishop sent a thumping header past Brain at the death.
There was still time for Ismail Yakubu to see his effort cleared off the line, but Macclesfield held on to take a point.