Rankin began his professional career in 2006 by starring alongside Robert Florence in VideoGaiden, a Scottish video game show originally aired on BBC Two Scotland.
Between 2007 and 2010 he made appearances on episodic Scottish television programs Legit (2007) and The Old Guys (2009) for the BBC and Taggart (2010) for STV.
The Scottish sketch comedy series Burnistoun, which premiered in 2009 and ran for three series on BBC Two Scotland, featured Rankin in various roles.

Two years later Rankin was cast as lovelorn Army Captain Thomas Gillan, alongside Kevin Doyle and Oona Chaplin, in the WWI based mini-series The Crimson Field .
The program aired on BBC One in April 2014, but only ran for one series.
He joined the cast of BBC One's crime drama series Silent Witness in January 2015, starring as Detective Inspector Luke Nelson in series eighteen's two-part story "Falling Angels".
The episode focused on a series of murders on the London Underground, the investigation of which brought up mysterious childhood memories of his father's murder.
Rankin went on to guest star in two episodes of NBC's conspiracy thriller American Odyssey as corporate hit man Haney, though the series was cancelled after season one.

Writer Kay Mellor tailored the role of Sean McGary for Rankin, changing the character from a Northerner to a Scot, in 2015's third series of her anthology drama The Syndicate.
The series followed a group of colleagues who win the lottery, with Rankin portraying the gamekeeper of struggling English manor Hazelwood.
That same year, BBC One's four part crime drama From Darkness saw Rankin portray Norrie Duncan, husband to Anne-Marie Duff's ex-Manchester cop Claire Church.

December 2015 brought the announcement that Rankin had been cast as adult Roger Wakefield in Starz's time-traveling drama series Outlander, which is based upon Diana Gabaldon's best-selling book series.
Appearing first in the 2016 season two finale and then again in several episodes of season three, Rankin's character is the love interest of Brianna Randall Fraser.
He returned in season four, which premiered 4 November 2018, with an expanded and recurring role in the series.
Later in 2016, Rankin appeared as Detective Inspector Elliott Carne on the BBC's crime drama Thirteen.
The series centered on Ivy Moxam (Jodie Comer), a young girl kidnapped and held for thirteen years, as she attempted to reconnect with the life she once had.

Rankin had roles in two BBC productions in 2017.
First was the dramatic miniseries The Replacement, which revolved around Ellen (Morven Christie), who was dealing with maternity leave and the effects it was having on her career.
Rankin played her psychiatrist husband in the three part series.
The second was a two episode stint as Father Hrothweard in BBC Two's historical drama The Last Kingdom, which was based upon Bernard Cornwell's series of novels entitled The Saxon Stories.

Series twenty of ITV's long-running crime drama Midsomer Murders, which premiered in the United States in 2018 prior to its release in the UK, featured Rankin in episode four as rugby star Danny Wickham.
In 2019 Rankin starred in series two of BBC One's drama Trust Me as neurologist Dr. Alex Kiernan.
The second series, which began filming in Glasgow, Scotland in September 2018, featured a complete recasting from series one, with Rankin joining Alfred Enoch, Ashley Jensen, and John Hannah in the medical thriller.

In July 2020, Rankin starred in an episode of the National Theatre of Scotland/BBC Scotland's Scenes for Survival, a series of short theatrical productions that were filmed in quarantine, which was created in response to a worldwide outbreak of COVID-19.
The episode, entitled The Longest Summer, features Rankin as a man remembering his childhood summers, and includes a title song written by Noisemaker and performed by Rankin.
The song was later released as a single to raise funds for the Scenes for Survival Hardship Fund, which assists artists hardest hit by the pandemic.
Rankin began his professional career in 2006 by starring alongside Robert Florence in VideoGaiden, a Scottish video game show originally aired on BBC Two Scotland. Between 2007 and 2010 he made appearances on episodic Scottish television programs Legit (2007) and The Old Guys (2009) for the BBC and Taggart (2010) for STV. The Scottish sketch comedy series Burnistoun, which premiered in 2009 and ran for three series on BBC Two Scotland, featured Rankin in various roles.
Two years later Rankin was cast as lovelorn Army Captain Thomas Gillan, alongside Kevin Doyle and Oona Chaplin, in the WWI based mini-series The Crimson Field . The program aired on BBC One in April 2014, but only ran for one series. He joined the cast of BBC One's crime drama series Silent Witness in January 2015, starring as Detective Inspector Luke Nelson in series eighteen's two-part story "Falling Angels". The episode focused on a series of murders on the London Underground, the investigation of which brought up mysterious childhood memories of his father's murder. Rankin went on to guest star in two episodes of NBC's conspiracy thriller American Odyssey as corporate hit man Haney, though the series was cancelled after season one.
Writer Kay Mellor tailored the role of Sean McGary for Rankin, changing the character from a Northerner to a Scot, in 2015's third series of her anthology drama The Syndicate. The series followed a group of colleagues who win the lottery, with Rankin portraying the gamekeeper of struggling English manor Hazelwood. That same year, BBC One's four part crime drama From Darkness saw Rankin portray Norrie Duncan, husband to Anne-Marie Duff's ex-Manchester cop Claire Church.
December 2015 brought the announcement that Rankin had been cast as adult Roger Wakefield in Starz's time-traveling drama series Outlander, which is based upon Diana Gabaldon's best-selling book series. Appearing first in the 2016 season two finale and then again in several episodes of season three, Rankin's character is the love interest of Brianna Randall Fraser. He returned in season four, which premiered 4 November 2018, with an expanded and recurring role in the series. Later in 2016, Rankin appeared as Detective Inspector Elliott Carne on the BBC's crime drama Thirteen. The series centered on Ivy Moxam (Jodie Comer), a young girl kidnapped and held for thirteen years, as she attempted to reconnect with the life she once had.
Rankin had roles in two BBC productions in 2017. First was the dramatic miniseries The Replacement, which revolved around Ellen (Morven Christie), who was dealing with maternity leave and the effects it was having on her career. Rankin played her psychiatrist husband in the three part series. The second was a two episode stint as Father Hrothweard in BBC Two's historical drama The Last Kingdom, which was based upon Bernard Cornwell's series of novels entitled The Saxon Stories.
Series twenty of ITV's long-running crime drama Midsomer Murders, which premiered in the United States in 2018 prior to its release in the UK, featured Rankin in episode four as rugby star Danny Wickham. In 2019 Rankin starred in series two of BBC One's drama Trust Me as neurologist Dr. Alex Kiernan. The second series, which began filming in Glasgow, Scotland in September 2018, featured a complete recasting from series one, with Rankin joining Alfred Enoch, Ashley Jensen, and John Hannah in the medical thriller.
In July 2020, Rankin starred in an episode of the National Theatre of Scotland/BBC Scotland's Scenes for Survival, a series of short theatrical productions that were filmed in quarantine, which was created in response to a worldwide outbreak of COVID-19. The episode, entitled The Longest Summer, features Rankin as a man remembering his childhood summers, and includes a title song written by Noisemaker and performed by Rankin. The song was later released as a single to raise funds for the Scenes for Survival Hardship Fund, which assists artists hardest hit by the pandemic.
Richard Rankin