It was a Group G clash that the Hoops were not supposed to win but the East End of Glasgow exploded in the 21st minute when midfielder Victor Wanyama headed in from a Charlie Mulgrew corner.
The home side had to defend for most of the night as the star-studded visitors hit the woodwork twice and keeper Fraser Forster pulled off a couple of vital saves.
However, in the 83rd minute 18-year-old Tony Watt, on for Mikael Lustig to make his debut in the group stages of the competition, raced away to score the second, leaving Lionel Messi's late strike a consolation.
Parkhead witnessed one of its greatest nights with pop singer and Celtic fan Rod Stewart captured in the main stand crying after the final whistle.
Hoops boss Lennon, though, could hardly suppress his joy, saying: "I think it was one of the greatest nights in the club's recent history.
"It was very poignant at our 125th anniversary, one to play Barcelona in such a prestigious game and two, to win the game under huge difficulties with the squad decimated by injuries and illness.
"The players are heroes, they are heroes to me, I can't speak highly enough of their performance tonight [Wednesday] and they will go down in the history books of the club as the team who beat probably the best team in the world.
"Everyone goes on about tactics but football is about players and they have covered themselves in glory tonight [Wednesday]."
"Seriously, when Tony Watt scored the second goal in 83 minutes, I turned round to my assistant Johan (Mjallby) and said 'I think we might get a point out of this game'.
"The legs of some players were starting to go a little bit and they (Barca) just wear you down.
"They keep coming and keep coming but it was a remarkable effort.
"We had to dig deep. It meant so much to so many people and it is a boost for Scottish football considering all the negative press we have had over the last six months.
"I told them before the game that this was their moment, make the most of it.
"At the Nou Camp we defended valiantly and came away with nothing and before the game I said, 'don't be gallant losers again, use that as motivation. You know what's coming, know you are going to lose possession and be under pressure, can you see it out this time?'
"To be fair, we got the breaks at the right time.
"I told them to enjoy it because they had done something very special."
Celtic, with seven points from four games, two less than leaders Barca, travel to Benfica before hosting Spartak Moscow in their final group fixture.
Benfica have four points following their home win over Spartak Moscow, who are bottom of the group with three points.
"At the end of the day we haven't done anything yet, we haven't qualified." Lennon said
"I said judge us over six games and we have given ourselves a great platform.
"What it means is that Barcelona still have to get something out of the next two games which benefits us.
"They will have to get a point or maybe three out of the two remaining games which is great because they could have had 12 points after last night [Wednesday] if they had beaten us and could have chopped and changed in the remaining two games.
"It gives us a foothold to get something at Benfica or against Spartak Moscow in the last game and really, that is all we could have asked for going into this competition."
The Hoops fans will surely fancy their side's chances of reaching the knockout stages of the competition but Lennon remained cautious.
The former Celtic skipper said: "We have a chance, that's all it has given us. A greater chance than maybe we expected before the game.
"But we still have two very tough games.
"The problem is the players and staff will have to deal with is that the expectation level will increase.
"There is still a lot of work to do but we have given ourselves a platform.
"But that's for the future, I want the players to enjoy the moment and take it all in."
Lennon praised the inexperienced Watt who is fast becoming a favourite of the Celtic fans.
He said: "It is a memorable thing he has done so early in his career.
"I said before the game I had no hesitation in playing him, I just thought his lack of experience would have been too much to put him in the starting line-up but everything we asked him to do, he did.
"He scored a brilliant goal and should have had a penalty and a sending-off when he got on Mascherano's wrong side.
"He is learning, he wrote himself into the history books of the club but he is 11 games into his career.
"I hope he has a fruitful career but tonight [Wednesday] will take some topping."
As they did when they came back from a goal behind in the Nou Camp last month to win 2-1 against Celtic, Barcelona dominated possession.
However, this time their superiority was confined to everything but the most important part of the game - goals.
Barca coach Tito Vilanova said: "First of all I would like to congratulate Celtic, the fans were amazing tonight [Wednesday].
"Before we played I knew they were good at set-pieces and we didn't want to concede too many and we didn't give them too many chances.
"But I can't be satisfied because we want to win the game.
"It is a really difficult stadium but we were like the home team and we locked them in the box.
"But you are never happy when you don't win.
"If we had scored first it might have been a different game.
"But they scored first which allowed them to defend and their goalkeeper was brilliant tonight [Wednesday].
"It is not the first time we have lost a game like this and it won't be the last."