The first appearance of Holmes, 1887
Explicit details about Sherlock Holmes's life outside of the adventures recorded by Dr. Watson are few and far between in Conan Doyle's original stories; nevertheless, incidental details about his early life and extended families portray a loose biographical picture of the detective.
An estimate of Holmes' age in the story "His Last Bow" places his birth in 1854; the story is set in August 1914 and he is described as being 60 years of age. Commonly, the date is cited as 6 January. However, an argument for a later birthdate is posited by author Laurie R. King, based on two of Conan Doyle's stories: A Study in Scarlet and "The Gloria Scott" Adventure. Certain details in "The Gloria Scott" Adventure indicate Holmes finished his second and final year at university in either 1880 or 1885. Watson's own account of his wounding in the Second Afghan War and subsequent return to England in A Study in Scarlet place his moving in with Holmes in either early 1881 or 1882. Together, these suggest Holmes left university in 1880; if he began university at the age of 17, his birth year would likely be 1861.
Holmes states that he first developed his methods of deduction while an undergraduate. The author Dorothy L. Sayers suggested that, given details in two of the Adventures, Holmes must have been at Cambridge rather than Oxford and that "of all the Cambridge colleges, Sidney Sussex (College) perhaps offered the greatest number of advantages to a man in Holmes’ position and, in default of more exact information, we may tentatively place him there".
His earliest cases, which he pursued as an amateur, came from fellow university students. According to Holmes, it was an encounter with the father of one of his classmates that led him to take up detection as a profession, and he spent the six years following university working as a consulting detective, before financial difficulties led him to take Watson as a roommate, at which point the narrative of the stories begins.
From 1881, Holmes was described as having lodgings at 221B, Baker Street, London, from where he runs his consulting detective service. 221B is an apartment up 17 steps, stated in an early manuscript to be at the "upper end" of the road. Until the arrival of Dr. Watson, Holmes worked alone, only occasionally employing agents from the city's underclass, including a host of informants and a group of street children he calls "the Baker Street Irregulars". The Irregulars appear in three stories: "A Study in Scarlet," "The Sign of the Four," and "The Adventure of the Crooked Man".
Little is said of Holmes's family. His parents were unmentioned in the stories and he merely states that his ancestors were "country squires". In "The Adventure of the Greek Interpreter", Holmes claims that his great-uncle was Vernet, the French artist. His brother, Mycroft, seven years his senior, is a government official who appears in three stories and is mentioned in one other story. Mycroft has a unique civil service position as a kind of memory-man or walking database for all aspects of government policy. Mycroft is described as even more gifted than Sherlock in matters of observation and deduction, but he lacks Sherlock's drive and energy, preferring to spend his time at ease in the Diogenes Club, described as "a club for the most un-clubbable men in London".
A portrait of Sherlock Holmes by Sidney Paget from The Strand Magazine, 1891 in "The Man with the Twisted Lip".
Life with Dr. Watson