The story begins in 1937, the same year Colchester United was founded, when a group of local enthusiasts established the Colchester Repertory Company. Repertory in the British sense meant a resident ensemble producing a different play every fortnight - or every week, in punishing periods - drawing audiences from the town and from the army garrison that has shaped Colchester for two thousand years. The Rep performed in a small theatre on Albert Hall site, putting on the kind of varied bill - drawing room comedies, Shakespeare, an Agatha Christie or two each year - that kept regional theatre alive in mid-century England. By the late 1960s the original venue was tired, and the company's ambitions had outgrown it. In 1968 the Colchester New Theatre Trust formed with one task: find a site, raise the money, build something better.

The architect Norman Downie produced a design that, by quirk of commission, was structurally identical to the Salisbury Playhouse he was building at the same time. Two near-twin theatres opened within months of each other - though Salisbury would later extend its version. The Mercury opened on 10 May 1972. The borough council had funded a large share of the build; the rest came from a community fundraising drive that involved everything from raffles to civic dinners. Downie's design gave Colchester a main house, a studio space, and an unobstructed sightline from anywhere in the auditorium. The building is unfashionable now - concrete and dark brick are not the favourite materials of the present moment - but the proportions of the spaces inside have aged well. A stage at the Mercury feels intimate even when the room is full.

Producing theatres are defined by the people who run them, and the Mercury has had a steady series of artistic directors. David Buxton opened the building. Michael Winter took over in 1984, eventually becoming Chief Executive as well as Artistic Director. Pat Trueman led the company through the mid-1990s. Dee Evans arrived as Chief Executive in 1998, working with Gregory Floy as Artistic Director, and together in 1999 they formed the Mercury Theatre Company, the producing brand that defined the building's output for over a decade. In 2012 Daniel Buckroyd and Theresa Veith took over and introduced 'Made in Colchester' as the new label for the theatre's own productions. A 2019 restructure put Tracey Childs and Steve Mannix in as joint Chief Executives with Ryan McBryde as Creative Director. In January 2025 Natasha Rickman was appointed Artistic Director, the latest hand on a tiller that has been steady for more than half a century.

What sets the Mercury apart is its commitment to making rather than only presenting. Mercury Originals - and its successor brand Made in Colchester - have produced new plays, revivals and musical adaptations that travel beyond Essex. Recent decades have seen well-reviewed productions of The Butterfly Lion, The Hired Man, Devil's Advocate and the First World War play Journey's End. National critics make the trip; the Financial Times, the Guardian and the Telegraph have all reviewed productions here. The theatre also runs a Community Education Programme, founded by Adrian Stokes after he joined as Associate Director in 1995, which trains young performers and brings school groups into the building. The Digby Gallery, until recently set in the foyer, exhibited work by Essex artists. In a town that already balances Roman ruins, a Norman castle, garrison soldiers and a university, the Mercury sits as the place where Colchester sees and writes about itself.