Rankin was born Richard Harris in Rutherglen in 1983 and attended Stonelaw High School in the town, although he was raised in the Glasgow districts of Hillhead and King's Park.
Rankin first came to prominence with Robert Florence, starring alongside him in VideoGaiden and Burnistoun. After brief appearances on Scottish television shows such as Taggart and Legit, he was approached by the BBC to star as Captain Thomas Gillan in a mini-series called The Crimson Field alongside Kevin Doyle and Oona Chaplin. The series aired on BBC One on in April 2014. He also starred in a low-budget horror film, House of Him, which was released during the Glasgow Film Festival in February 2014. The film had a budget of approximately £900 and starred many of his old Burnistoun colleagues, including Robert Florence, Kirsty Strain and Louise Stewart.
In January 2015, Rankin joined the cast of the BBC One crime drama series Silent Witness in the two-part story "Falling Angels", playing Detective Inspector Luke Nelson. In December of the same year, it was announced that Rankin had been cast as Roger Wakefield in the Starz series Outlander.
