The London-based practice has seen off nearly 230 other submissions to win the Kielder Observatory Competition.
The office - which had to respond to the challengingly small budget of £125,000 - beat five other shortlisted entries, including the trio of Kevin Carmody, Andy Groarke and Chris Hardie, who recently won the international Coney Island parachute jump competition.
Barclay's designs, which he worked up with a local astronomer, were praised by the jury for blending 'innovative design' and 'essential practicality'.
Barclay was unsurprisingly ecstatic at the outcome. 'We are exhilarated to have won the competition for the observatory at Kielder and acknowledge the input of our co-collaborators, particularly the astronomer in residence at Marlborough College, whose name is also Charles Barclay,' he said.
'It is an honour to be entrusted with the latest of a series of interesting commissions by the Kielder Partnership and we relish the challenge of designing an architectural piece that is resonant in its wild setting yet fulfils a technically demanding brief,' he added.