The man behind theatre groups 7:84 and Wildcat, and the internationally renowned A Play, A Pie and A Pint series at Oran Mor in Glasgow, Maclennan is a respected figure in Scottish theatre.
Maclennan, who this week revealed he was living and working with motor neurone disease, has written a humorous poem, If Scotland, which gives his wry perspective on Scottishness and whether it would be altered by a yes vote in the referendum.
"If we vote yes," asks the poem, "Will the Proclaimers rediscover their Dundee accents/Will Phil Cunningham get his act together on that box of his/And Aly Bain get to grips with his Shetland fiddle/Will Paolo Nutini sound more Paisley/And Capercaillie a bit more Gaely".
Explaining why he wrote it, Mr Maclennan said Scottish culture was thriving within the UK: "It's always struck me that Scotland has an extraordinarily strong and powerful culture. All kinds of things contribute to that - geography, landscape, language, football."
He is one of relatively few high profile artistic figures in Scotland to come out for the No camp, but the list includes some big names such as JK Rowling, Sharleen Spiteri, Susan Boyle and the actress Emma Thompson, who lives part of the year in Argyll.
Mr Maclennan said: "I've worked all over England touring plays, all my family live in London and I have friends all over the UK.
"Being of a left-wing persuasion, I'm very mindful of the links of the Labour movement. I don't feel there's much difference between Glasgow and Liverpool or Manchester.
"I think those on the pro-union side perhaps haven't voiced their passions as eloquently as those on the independence side."
He said that in an increasingly globalised society "the more borders we can get rid of, the more peaceful the world will be". Mr Maclennan is working with playwright David Greig,an independence supporter, co-curating the National Theatre of Scotland's The Great Yes No Don't Know Five Minute Theatre Show, encouraging the public to produce five-minute referendum-themed performances.