The London-based practice beat hatfuls of hopefuls to land the £125,000 project back in December last year with its 'innovative' and 'practical' design.
Almost 230 practices - including 60 overseas firms - entered the hugely popular contest, which was dubbed the 'biggest in Britain for a generation.'
The winning design was drawn up with a local astronomer who, coincidentally, is also called Charles Barclay.
Construction of the pier-like building on top of Black Fell, is due to start in September. It is hoped that the first stargazers will be able to visit the completed observatory early next year.
An exhibition showcasing the design will be on display in the Queens Hall, Hexham, Northumberland until 1 July.