MacLennan was born on 19 June 1948 to Isabel Margaret (née Adam), a doctor and public health activist, and Sir Hector MacLennan, a renowned gynaecologist and obstetrician.
MacLennan co-founded the Scottish left-wing agitprop theatre group 7:84 in 1971, with his sister Elizabeth and her husband John McGrath.
In 1978 he created the influential Wildcat Stage Productions (with Dave Anderson) and worked with these two companies for most of his life.
[2][3][4] In 2004, MacLennan created A Play, a Pie and a Pint at the Òran Mór in Glasgow; a lunchtime theatre concept which has since been implemented around the world.
[6] In 2013, MacLennan was diagnosed with motor neurone disease, dying in hospital in Glasgow the following year, aged 65.