When Does "Peaky Blinders" Season One (2013) Take Place?

"Peaky Blinders" season one is a crime historical fiction television show showran by Steven Knight that released on September 12th, 2013. 

It takes place in the year: 

1919 AD 

We know this because numerous vague references in dialogue and a set of files held by Chief Inspector Chester Campbell (loosely based on the real-world Birmingham Chief Constable Charles Haughton Rafter [1860-1935]) in season 1 episode 1 make it clear that several characters have recently returned from fighting in France. The phrase "since the war" is spoken several times. About halfway through the episode, Campbell says, "Those of you who have taken their bribes these years since the war"... 

Then, in season 1 episode 2 Johnny Dogs asks Thomas "Tommy" Shelby, "So, your first fair since France?" implying the first of a reoccurring event since their return from this war is happening. Later in the same episode, Tommy declares, "I won gallantry medals at the Somme.", referring to the Battle of the Somme, a pivotal battle of World War I. The recent war must be World War I, which ended in November of 1918 AD so it must be after late 1918 AD. 

More specifically, the real-world British politician Winston Churchill (1874-1965) appears about three-quarters into season 1 episode 1 and is introduced as "Secretary of State", therefore it must take place sometime during his time as Secretary of State for War and Secretary of State for Air, which lasted from January 10th, 1919 AD to February 13th, 1921 AD. So it must be after or during early 1919 AD and before or during early 1921 AD. 

Finally, in season 1 episode 2 Elizabeth Pollyanna "Aunt Pol" Gray is reading an issue of the real-world "The Birmingham Evening Despatch" (known as "Birmingham Mail" since 2005 AD) dated for "MONDAY, 3 MARCH, 1919". The season therefore begins in early 1919 AD since this episode clearly takes place partially on March 3rd, 1919 AD. 

Furthermore, the second scene of season 1 episode 1 includes a time and place setting title card over the footage that reads "BIRMINGHAM, ENGLAND 1919". 

Season 1 episode 6 depicts events the characters refer to as Black Star Day, which Tommy marks on a calendar in season 1 episode 5. The day marked with a black star is December 3rd. So the season finishes in December of 1919 AD. 

HOWEVER, the events of Black Star Day are a dramatized (with a reversed outcome) version of an outcome in the feud between the real-world Peaky Blinders gang and the real-world Birmingham Boys gang that happened in 1920 AD. 

This Looper article examines the show's exact setting. 

and 

This West Midlands History video examines the show's historical changes.