|Portrayed by||Wil Johnson|
|First Appearance (Regular)||Series 6 Episode 1|
|Last Appearance (Regular)||Series 6 Episode 10|
|First Appearance (Guest)||Series 6 Episode 19|
|Last Appearance (Guest)||Series 6 Episode 20|
|Cause/Reason||Resigns (First Stint)|
Leaves Waterloo Road when he believes it to have failed his son (Guest)
|Grandchildren||Jonah and Francesca Montoya's unborn child|
Marcus Kirby is a former academic and the driving force behind the Kirby family’s previous decision to home-educate Jonah and Ruth. Marcus home-educated out of pride and ambition, quantifying life success as academic success and he’s afraid that Waterloo Road will wipe out all of his brilliant work and harm his children’s bright future. As they start at the school Marcus is determined that his children will return to home-schooling, but when Karen brings him in for a review of their progress Marcus is surprised to find her also offering him a job in the Geography department. She’s seen his dynamism with pupils and wants to harness it at the school. Marcus has a long way to go in conquering his prejudices against the state system but no one can deny he’s a great teacher. He and Karen had a good relationship, connecting over their love for education and shared experiences with ex-partners.
After it is revealed in Series 6 Episode 9 that before the academic year started Chris Mead slept with Karen's daughter Jess Fisher, the girlfriend of Marcus' son Jonah, Marcus demands that Karen sack him and threatens to walk out if she doesn't. After making Chris promise that he would learn from his inexperience in the role Karen welcomes him back to Waterloo Road, causing Marcus to leave, though he and Karen later reconcile. He is later shocked to learn that Ruth wants to stay at the school instead of going to a private school after she did well in her admissions test, but is supportive of her decision. Karen said the door was always open for him to return as a teacher, and she once mentioned to Chris that Marcus probably would have become Deputy Head if he had refused to come back.