Lennon's men took a 2-0 lead into the second leg of their play-off against the Swedish side and Gary Hooper's close-range strike on the half-hour mark effectively ended the contest before Victor Wanyama grabbed the second two minutes from time.
Asked how he would describe the result with regards his managerial career, the Hoops boss said: "It is the best. I have been to hell and back in the last seven weeks trying to get this right."
He went on: "There is a fear factor and I lived with that. I am thinking of the ramifications if we don't go through, what it would mean for me personally, how I would get through it and how I would get over it.
"That was part of the build-up. Everyone had us in the Champions League but in the back of your mind there is always that worry, that fear.
"We have overcome that and dealt with the two qualifiers very well
"It is a great night for me personally and a great night for the players. It is not often I pat myself on the back but I am going to tonight.
"It is one of the hardest challenges I have ever had in my life and the pressure going into this game was huge. I have never experienced that in my playing days and I am so happy
"It is a minor miracle we qualified. The squad is so thin but we have a good core of players and I am very proud of them."
The draw for the group stage takes place on Thursday afternoon.
Premier League club Arsenal are the only club not to have won the Champions League to be placed among the top seeds.
Arsene Wenger's side were granted a place in the top eight based on what UEFA called their 'coefficient', based on previous performances in the competition.
Holders Chelsea, Barcelona, Real Madrid, Manchester United, Porto and AC Milan are also amongst the top seeds waiting to find out which one of the eight groups they will be drawn into.
Of the 32 teams in the draw there are 12 former winners and three teams making their debut in the tournament.
Celtic became the last former European champions to make it through to the group stage and will be in pot four in the seedings.
Malaga of Spain, Montpellier of France and FC Nordsjylland, the Danish champions, are all competing for the first time.
Teams from the same country cannot be drawn against each other in the group stage.
Pot one: Chelsea, Barcelona, Manchester United, Bayern Munich, Real Madrid, Arsenal, Porto, AC Milan
Pot two: Valencia, Benfica, Shakhtar Donetsk, Zenit St Petersburg, Schalke, Manchester City, Braga, Dynamo Kiev
Pot three: Olympiacos, Ajax, Anderlecht, Juventus, Spartak Moscow, Paris St Germain, Lille, Galatasaray
Port four: Celtic, Borussia Dortmund, BATE Borisov, Dinamo Zagreb, FC Cluj, Malaga, Montpellier, FC Nordsjylland
- Victor Wanyama