Robertson is not gay. Robertson has two children with his Norwegian wife Mille Fjelldal, whom he met in 2008 and married in August 2021. Fjelldal had been due to give birth to the couple’s first child while Robertson was playing in the 2010 World Championship final, but their son Alexander was not born until the 12th of May 2010. Their daughter Penelope was born on 16 March 2019.
Robertson has spoken publicly about supporting his wife through her struggles with anxiety and depression, while also acknowledging how these issues affected his commitment to professional snooker.
Robertson has been a vegan since 2014. He began to pursue a plant-based diet following advice from fellow snooker professional Peter Ebdon as well as his admiration for vegan athlete Carl Lewis.
Robertson is a friend of former England footballer John Terry and is an avid supporter of Chelsea FC. In June 2016, he became the ambassador of the electronic snooker simulator app Snooker Live Pro. He was an avid gamer but gave up the hobby in April 2017, believing he was spending too much time playing games and it was affecting his snooker form.