The term micropub was originally devised by the Campaign for Real Ale, in the 1976 edition of its Good Beer Guide, simply as a description for an unusually small but otherwise traditional pub. Examples of pubs described as such in this era included Manchester's Circus Tavern and The Nutshell in Bury St Edmunds. In more recent years, the term came to be redefined much more tightly, as a very small, modern, one-room pub, serving no food other than snacks, and "based upon good ale and lively banter". The original of these newly defined micropubs is often cited as the Butchers Arms in Herne, Kent.

According to the Micropub Association, an organisation set up in 2012, a micropub is now defined as follows: "A micropub is a small freehouse which listens to its customers, mainly serves cask ales, promotes conversation, shuns all forms of electronic entertainment and dabbles in traditional pub snacks". The Micropub Association goes on to explain that a micropub may or may not have a bar, and might serve beer straight from the cask or through hand pumps, but share a philosophy: a simple pub with the focus on cask beer and conversation for entertainment.

This modern definition is not accepted by all pub campaigners, many of whom continue to use the term micropub simply to refer to any unusually small public house.

It became easier to set up a small independent pub in the United Kingdom following the passing of the 2003 Licensing Act, which became effective in 2005.

The Butchers Arms in Herne, Kent, was opened in 2005 by Martyn Hillier after spending several years as an off-licence, and to describe this new and novel style of pub, Hillier resurrected the term "micropub". In 2009, Hillier gave a presentation to the AGM of Campaign for Real Ale, in Eastbourne, outlining what he considered to be the simplicity of this new micropub model and encouraging other people to consider opening similar type establishments.

It proved to be a catalyst, with the Rat Race Ale House in Hartlepool six months later and Just Beer Micropub in Newark-on-Trent opening August 2010, soon after followed by The Conqueror Alehouse the same year. Since then, there have been several more micropubs opening such as The Just Reproach in Deal, Kent and the Bake & Alehouse in Westgate-on-Sea, Kent.

In June 2012, the Micropub Association was set up by Hillier along with Stu Hirst, as a resource for other would-be micropubs and to give free advice on the setting up and running of a successful micropub. Hillier wrote on his website:

"The Micropub Association will be a place where like-minded real ale lovers can share their micropub experiences. The Micropub Association will also be a platform for the new Micropubs to tell the beer drinking community about themselves. A successful Micropub is based upon good ale and lively banter and I want this to come across through the Micropub Association. Ultimately I’d like to think that we could become a useful lobby group to support the likes of CAMRA and SIBA, promoting the real ale experience".