The BBC drama, which is set in the 1930s, follows a teacher called Sarah (Anna Maxwell Martin) as she becomes the head at a Yorkshire girls' school.
Speaking to What's On TV, Morrissey explained that his character Robert will be unhappy about Sarah's arrival.
"Robert is a middle-class landowner who is on the local council and takes his duties seriously," he said. "Sarah has strong views about the education of women whereas Robert's a traditionalist, so she starts off rubbing him up the wrong way."
Morrissey described the drama as a "rollicking great story about unrequited love and social conscience", adding: "It's relevant to a modern audience, too, as it's set in a time of economic hardship."
South Riding begins on Sunday at 9pm on BBC One.