Hundreds of actors, writers, producers and theatre technicians appeared to pay their respects to MacLennan, to offer colour and insight to a life that impacted on so many.
MacLennan, who had been suffering from Motor Neurone Disease, had been one of the founder members of iconic Scottish theatre in the form of 7:84 Theatre Company and Wildcat, both of which changed the very perception of the art form.
But the 65-year-old's life work also produced a remarkable third act in the form of Oran Mor lunchtime theatre experience, A Play A Pie and A Pint.
A piper played as mourners including playwright and artist John Byrne and actors Dave Anderson and Colin McCredie entered Clydebank Crematorium.
Gregor Fisher, Elaine C Smith, and Still Game stars Greg Hemphill and Ford Kiernan also turned out to pay their respects.
Mr MacLennan's son Shane read a poem written by his father during the service and everyone joined in with a performance of the Robert Burns song A Man's A Man For A' That.
MacLennan's brother, Robert, spoke at the service of the 'community of affection for an exceptional human being' which David MacLennan certainly was. "David had an exceptional capacity for understanding the human condition and that was revealed in his life's work and dedication to the theatre," he said.
David's second brother Kenneth spoke of the family's life - the parents were both doctors, growing up in the West End of Glasgow. And he highlighted how young David was a unique individual.
"The entertainer Jimmy Logan lived next door to us, and he became an uncle to us. And I remember once he was in our house during our parents' silver wedding anniversary and Jimmy performed a This Is Your Life sort of sketch. His performance began 'Hector and Isabel MacLennan were blessed with three children - and David."
Young David was certainly a unique character, highlighted when he fell in love with theatre the day he went to the King's Theatre in Glasgow and saw Peter Pan.
"When Peter Pan called out to the audience - to save Tinkerbell - 'Do you you believe in Fairies? We all stood up and said 'Yes'. But outside the theatre, David carried on asking the question of adults. He was mesmerised by the theatre world."
MacLennan's best friend and colleague Dave Anderson retraced their life together, from 7:84 days to Wildcat. He spoke of how his friend had continued his love for theatre while performing in plays at public school.
"David's family expected him to become a doctor, but that wasn't for him. He was interested in politics, in people, and theatre. After attending Edinburgh University he became a bin man for a while."
He added, grinning: "Edinburgh lost a very promising bin man when David went into the theatre world."
Anderson spoke of his chum's love for theatre life, for touring plays round the Highlands, for performing and whisky, sometimes both enjoyed at the same time.
He spoke of how his friend's love for theatre production had been formed while watching the variety theatre of the late 1950s, to which he would later add a political sensibility, described by actor Bill Paterson as 'Marxist-MacLennanist.'
Dave Anderson spoke of his friend's humanity, his vision and his talent. He said he didn't know if the idea for the now international success story A Play, A Pie and A Pint came off the top of his head the day David met Oran Mor's boss Colin Beattie. Or if it had been lingering for some time.
"You could never be sure," he said, "but David was always coming up with ideas, backed by incredible enthusiasm. My relationship with David involved me always saying 'Sure'. And I followed his lead."
Anderson revealed how MacLennan had been working on his autobiography but never managed to complete it.
Yet, those who gathered to commemorate - and celebrate - the life of MacLennan knew that didn't matter too much. Tales of his life would continue to be passed around for years to come.
"And you only have to look to see some of the most famous stars in Scottish showbiz in the restricted viewing area here today," added Dave Anderson, smiling, " to see the sort of impact the man made to Scottish theatre."
Anderson also revealed the darker colours of David MacLennan's personality; once in a fit of artistic temper he put his hand through a glass panel.
And he spoke of MacLennan's contempt for the arts council decision makers who cut Wildcat funding. "David labelled them 'ticket-rippers,'" he said, with a wry smile.
Anderson, at times choking back tears, echoed the thoughts of those gathered when he said that MacLennan's death 'hadn't sunk in yet.'
He spoke of how MacLennan and actress wife Juliet Cadzow, who married in 1988, were the 'perfect pair.' He laughed at the arguments he and MacLennan had over play content.
"David told me to write parodies, which I hated," he said. "It took me forty years, and listening to an awful lot of audience reactions, to realise he was right."
Anderson also had those gathered in stitches when he revealed the irony that, while MacLennan's parents had hoped their son would follow their lead and become doctors, he did in fact receive two doctorates from the RSAMD and Glasgow Caledonian University.
"When asked if he would like to be referred to hence forward as 'Doctor MacLennan' he replied, 'No, just call me Papa Doc-Doc.'"
Anderson finished his eulogy with a line which brought those gathered to tears.
"I want to thank David MacLennan on behalf of all those actors, directors, theatre technicians, producers and writers whom he has helped along the way."
So many knew they owed so much to one man.