The combative midfielder was deemed surplus to requirements by former boss Tony Mowbray and informed that he was free to move on.
Brown was able to ride out the storm, though, and has become an influential figure under Lennon.
The pair have enjoyed four successful years working together in Glasgow, with a third straight league title on the verge of being wrapped up.
Brown, who has been linked with a switch to England on a regular basis throughout his time at Celtic, could not be happier and will be eternally grateful to Lennon for handing him a clean slate.
Asked what the biggest thing the Bhoys boss has done for him, the Scotland international said: "He kept me here. He gave me a new deal and I'm still at a huge club."
Brown acknowledges, though, that things could have been very different, with Lennon revealing that he came close to walking away from his post after seeing Celtic fall three goals down to Kilmarnock in October 2011 - only to then hit back and claim a share of the spoils.
He added: "The manager would have been a huge loss, but thankfully he's still here.
"The gaffer knows what it takes to be a Celtic manager and what to expect. He knows not everyone is going to love him or the players, but he doesn't care about that. He only cares about the lads and what we do in that dressing room and on the park.
"The main thing is that he's a winner and he tries to put that into every individual, from the senior boys to the youngsters coming through."