Main •
David Thewlis as
Sherlock Holmes, a renowned private detective living at
221B Baker Street who seeks to uncover the mysterious criminal syndicate known as the Red Thread •
Blu Hunt as Amelia Rojas, a young American from
California who arrives in London following her mother's murder to find Sherlock Holmes, her suspected father •
Ardal O'Hanlon as Mr. Halligan, Sherlock's butler and coach driver •
Fiona Glascott as Lady Violet Somerset, a wealthy
socialite who trains young women in practising proper
etiquette in British high society •
Aidan McArdle as Chief Inspector Whitlock, the head of
Scotland Yard who is well acquainted with Sherlock • Kojo Kamara as Clarence Halfpenny, the owner of a carriage workshop •
Joe Klocek as Daniel "Dan" Moriarty, alias Michael Wylie, Professor Moriarty's estranged son and a juvenile offender who grew up in Australia •
Dougray Scott as
Professor James Moriarty, Sherlock's arch-enemy who is incarcerated at
Newgate Prison •
Owen Roe as
Lord Salisbury, the prime minister of the United Kingdom • Seán Duggan as
Dr. John Watson, Sherlock's closest friend and a skilled physician
Recurring • Mary O'Driscoll as Mrs. Halligan, Sherlock's temporary housekeeper • O'Driscoll also portrays
Mrs. Hudson, Mrs. Halligan's twin sister and Sherlock's landlady • Paul Reid as Inspector Bullivant, a senior police officer in charge of the investigation at the American ambassador's residence • Gia Hunter as Clara Anderson, the American ambassador's daughter, who befriends Amelia on the boat ride to England •
Phillip P. Keene as Paul Anderson, Clara's father and the newly-appointed
American ambassador to the United Kingdom •
Ivana Miličević as Marjorie Anderson, Clara's mother and Paul's wife • Aisling Kearns as Cassie, the Anderson family's maid • Savonna Spracklin as Lucia Rojas, Amelia's deceased mother and a proficient engineer who appears during flashbacks. Born Little Dove, her ethnicity is revealed in "For Kith and Kin" as "the daughter of a rancher and an
Apache, with a Spanish grandfather". • Orén Kinlan as Shaw McPherson, the leader of the
Baker Street Irregulars, a gang of street children whom Sherlock hires to find information • Shashi Rami as Bertram "Bertie" Birtwistle, an
insurance investigator searching for the American ambassador's missing jewels •
Antonio Aakeel as Detective Swann, part of the Scotland Yard scientific division, who is fascinated with the newest technological innovations
Guest • Hyoie O'Grady as Charles "Charlie" Holroyd, the Anderson family's coach driver •
Andy Kellegher as Weams, a criminal affiliated with the Red Thread • Michael Ellen Sean as Magott, Weams's partner, who is affiliated with the Red Thread • Caolan Byrne as Dankworth, a prison officer at Newgate Prison loyal to Moriarty • Jack Meade as Lord Withersea, a
nobleman working for the Red Thread •
Seamus O'Hara as O'Leary, Withersea's Irish bodyguard • Ruairí Heading as Pete Pound, a technician who installs a telephone at 221B Baker Street • Rose O'Neill as Emma, a
debutante under Lady Violet's tutulege • Maximilian Henhappel as Herr Bernt, an associate of Dan Moriarty • John Doran as Jeremy Stephens, Lord Salisbury's
private secretary ==Episodes==