"This is the greatest night of my football life," Lennon told Sky Sports News. "What we've come through in the last six weeks has been really difficult.
"We've lost three pivotal players over the simmer, which makes this achievement all the more remarkable."
Lennon was also quick to praise James Forrest, who scored the crucial third goal in stoppage time to send Celtic through.
"For some reason there is a section of our support that doesn't take to James Forrest," the Northern Irishman added.
"But he's a special player and he was magnificent tonight; they were all heroes."
The draw for the next round takes place tomorrow and Celtic will be in pot four.