Was in a relationship with Sofia Boutella (March 2014-October 2018).
His father was a member of Garda Siochana, the police force of the Republic of Ireland.
Currently resides in London, England and Los Angeles, California.
In 2017, a local newspaper in his hometown (Laois Today) published an article titled Moment in Time: Schoolboy Robert Sheehan wins his first movie role, in reference to his role in Mortal Engines (2018).
His elder brother, Brendan, is a mortgage broker and a director of Fitness Supplements.
He is the youngest of three children of Joseph and Maria Sheehan.
Robert Sheehan portrayed two characters who have similar powers, including immortality and seeing/speaking with the deceased. Klaus Hargreeves in The Umbrella Academy and Nathan Young in Misfits.