The annual stroll to the Scottish Premier League title in the last three seasons was viewed by his critics as more a reflection of a lack of credible opposition than Lennon's abilities in the dugout.
As Lennon's sudden departure from the club yesterday reverberated around the football world, there was speculation that off-field stress he faced may have played a role in his decision.
Perhaps no other figure in football faced the same pressures as Lennon, whose association with Celtic was accompanied by a catalogue of attacks on a man who was described by former Celtic player Andy Walker as the most "loathed, demonised and hated" figure ever in the sport north of the Border.
All too often, the depressingly familiar physical, verbal and psychological assaults on Lennon, a Northern Irish Catholic, bore the ugly hallmarks of sectarianism.
Enjoying a successful playing career in England, most notably at Leicester City under Martin O'Neill - who has a similar background to Lennon but has never attracted the same controversy - he signed for Celtic in 2000.
Playing for Northern Ireland in a friendly against Norway months later, he was subjected to sectarian abuse from his own fans.
Within two years, he had been forced to retire from international football after receiving a death threat from a figure claiming to represent a loyalist paramilitary group just before a friendly with Cyprus. Lennon, who was due to captain his country for the first time, pulled out of the game and announced shortly afterwards that he would not represent the province again.
"I can't put them [his family] through this every time," he said then, as the threat was condemned across Northern Ireland.
Earlier this year he said that before signing for Celtic his background had not been an issue when representing Northern Ireland.
Lennon's combative performances in the Celtic midfield saw him attract a reputation as a physical player - something he maintains was unwarranted.
But while a tough-tackling midfielder attracting the ire of opposition fans is not uncommon, abuse aimed Lennon was especially vitriolic.
In 2003, he was assaulted by two students and the following year vandals daubed graffiti outside his home.
"I had no things happen to me off the field in 14 years in England," he said recently. "So again, that's the association with being at Celtic. And there's no question, over the years there's been a huge sectarian element to what went on."
In 2008 he was left unconscious after being viciously assaulted in Glasgow's West End while walking home hours after an Old Firm game.
At the time he was a coach at Celtic, having returned to the club after finishing his playing career in England.
His two attackers repeatedly kicked him as he lay on the ground.
Rangers fans Jeffrey Carrigan and David Whitelaw were jailed for two years each for the assault, although they were cleared of an allegation the attack was aggravated by religious prejudice.
The most sinister threats, however, came after he became manager in 2010. In January 2011, he was sent a bullet in the post.
Four months later, parcel bombs addressed to Lennon and two high-profile Celtic fans were found soon after a touchline confrontation between Lennon and now Rangers manager Ally McCoist.
Two North Ayrshire men, Trevor Muirhead and Neil McKenzie, were jailed for five years each for their part in the bomb plot, after being found guilty of conspiracy to commit assault. Lennon's home was fitted with panic alarms.
Hearts fan John Wilson was jailed for eight months for breach of the peace after he confronted Lennon on the touchline at Tynecastle in May 2011.
Lennon hoped his problems were over after a personal bodyguard was hired to protect him.
But, in February, Aberdeen fans launched missiles at him as he watched a League Cup semi-final.